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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
A uniform chain has mass Mand length L. It is lying on a smooth horizontal table with half of its length hanging vertically downward. The work done in pulling the chain up the table is:A. `MgL//2`B. `MgL//4`C. `MgL//8`D. `MgL//16` |
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Answer» Correct Answer - C |
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| 52. |
An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path object lie on the same horizontal line. What is the work done by the force of gravity on the object ? |
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Answer» Correct Answer - Zero Work done by the force of gravity on an object depends only on vertical displacement. Vertical displacement is given by the difference in the initial and final positions/heights of the object, which is zero Work done by gravity is given by the expression, W = mgh Where h = Vertical displacement = 0 `W = mg xx 0 = 0 J` Therefore, the work done by gravity on the given object is zero joule. |
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| 53. |
A smooth narrow tube in the form of an arc AB of a circle of centre O and radius r is fixed so that A is vertically above O and OB is horizontal. Particles P of mass m and Q of mass 2 m with a light inextensible string of length (pi r/2) connecting them are placed inside the tube with P at A and Q at B and released from rest. Assuming the string remains taut during motion, find the speed of particles when P reaches B. .A. `sqrt((2gR)/(3))`B. `sqrt((2gR)/(3pi))`C. `sqrt((2(1 + pi) gR)/(3))`D. `sqrt((2pi gR)/(3))` |
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Answer» Correct Answer - C |
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| 54. |
Water stored in a dam possesses :A. no energyB. electrical energyC. kinetic energyD. potential energy |
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Answer» Correct Answer - D Water stored in a dam is at a height (h) from the ground level and its potential energy is given by, PE= mgh. |
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| 55. |
What type of energy is stored in the spring of a watch? |
| Answer» When we wind a watch, the configuration (shape) of the spring changes. The energy stored in the spring is obviously potential in nature (elastic potential energy to be more accurate). | |
| 56. |
Define avarage power. |
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Answer» Avarage power = `("total energy consumed")/("total time taken")` The concept of average power is useful when the power of an agent varies with time and it does work at different rates during different intervals of time. |
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| 57. |
How is energy stored in a clock ? |
| Answer» The energy stored in the clock is in the from of elastic potential energy of its coiled spring. The spring is coiled by winding the clock. | |
| 58. |
A woman lifts a box weighing 40N from the floor to a shelf 1.5 m above. (a) find the work done by the force (F) the woman exerts on the box (b) Find the work done on the box by its own weight (w) (c ) Find the net work done on the box. |
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Answer» (a) work done by the force F, i.e., `W_f = Fs = (40N) (1.5m) = 60J` (b) The weight of the box (w) acts ina direction opposite to the direction of motion. Thus, `W_w = - ws= - (40N)(1.5m) =-60J` (c ) Net work done on the box, `W_(net) = W_f +W_w =+ 60 J - 60J = 0` |
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| 59. |
The global climate has always fluctuated. Millions of years ago, some parts of the world that are now quite warm, were converted with ice, and over recent centries, average temperatures have risen and fallen in cycles. What is new, however, is that current and future climate change will be caused not just by natural events but also by activities of human beings. Suggest three simple ways to help save the climate of out planet. |
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Answer» 1. Drive less. Walk Carpoole or take Public Transport. You will save emission of 1.5 kg of `CO_2` for every 5 km you do not drive. 2. Use renewable energy. Use solar water heater instead of an electric geyser. A 100 litre solar water heater can sace around 1500 units of electricity every year. For lighting, use batteries that can be charged by sunlight. A solar cooker cooks food without losing its essential natrients. 3. Check your tyres. Keeping your tyres properly inflated improves the fuel efficiency of your vehical. Every litre of petrol saved, keeps 2.5 kg `CO_2` out of atmosphere. Using radial tyres will help you save 3% to 7% of fuel. |
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| 60. |
What kind of energy transformation take place in an electric fan and a loudspeaker ? |
| Answer» In an electric fan, electirc changes into kinetic energy. In a loudspeaker, electric energy changes into sound energy. | |
| 61. |
You lift a box weighing 200 N from the floor to a shelf 1.5 m above. (a) What is the maximum work done by the force you exert on the box ? (b) When would the work be greater then this maximum ? |
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Answer» (a) W = Fs = (200 N) (1.5 m) = 300 J (b) if you lift quickly by exerting a force greater then 200 ngt |
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| 62. |
What is 1 MJ ? |
| Answer» `1 MJ = 10^6J` | |
| 63. |
Why does a saw become warm when it is used to cut a log of wood ? State the energy transformation taking place. |
| Answer» A part of the KE of the saw gets converted into heat. | |
| 64. |
What is the origin of the word "kinetic"? |
| Answer» From the Greek word kinetikos which means to move. | |
| 65. |
A pair of bullocks exerts a force of `140 N` on a plough. The field being ploughed is `15 m` long. How much work is done in ploughing the length of the field? |
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Answer» Here, Work done, W = ? `" "` (To be calculated) Force, F = 140 N And Distance, s = 15 m Now, `W = F xx s` So, `W = 140 xx 15` W = 2100 J Thus, the work done in ploughing the length of field is 2100 joules. |
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| 66. |
(a) Which quantity provides a link between force and energy ? (b) What is the amount of work done in trying to move a huge rock but failing to do so? |
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Answer» (a) work. (b) zerol as the rock does not move with our effort (i.e., applied force). |
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| 67. |
A pair of bullocks exerts of work done on an onject when a force of 1 N displaces it by 1m along the line of action of the force. |
| Answer» Here,` F = 140 N , s = 15 m`. Work done in ploughing the field, `W = F xx = (140 N) xx (15 cm) = 2100 J` | |
| 68. |
How much energy is possessed by a moving body by virtue of its motion ? |
| Answer» If m is the mass of the moving body and `upsilon` is the velocity with which it moves, the energy possessed by it is given by `(1)/(2)m upsilon^2.` This is called the kinetic energy of the moving body. | |
| 69. |
(a) What is the cause of kinetic energy possessed by a body? (b) can kinetic energy of a body ever be negative? |
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Answer» (a) Motion of the body. (b) No. |
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| 70. |
Find the energy possessed by a bird of 5 kg moving at a constant height of 10 m from the ground with a speed of 2 m `s^(-1)`. (Take `g = 10 m s^(-2)`) |
| Answer» Correct Answer - PE = 500 J , KE = 10 J | |
| 71. |
An object of mass 15kg is moving with a uniform velocity of 4m/s. what is the kinetic energy possessed by the object ? |
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Answer» Correct Answer - A::B `E_k =(1)/(2)mv^(2) = (1)/(2)(15kg)(4m//s^2) = 120J` |
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| 72. |
Name a mechine that transforms muscular energy into useful mechanical work. |
| Answer» Answer:- Bicycle. | |
| 73. |
Find the energy possessed by an object of mass 10 kg when it is at a height of 6 m above the ground.Given, `g = 9.8 m//s ^2` |
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Answer» Mass of the object, `m = 10 kg`, displacement (height), `h = 6 m`, and acceleration due to gravity, `g = 9.8 m s^(-2)`. From Eq. (11.6), Potential energy = mgh `= 10 kg xx 9.8 ms^(2) xx 6m` = 588 J The potential energy is 588 J. |
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| 74. |
What do the mechines need fro their working ? |
| Answer» Since machines are meant to convert energy inot work, all mechines need energy for their working. | |
| 75. |
Why do some enignes require fuels like petrol and diesel ? |
| Answer» Internal combustion heat engines use the chemical energy of fossil fuels (petrol and diesel) for their operation. These engines first convert the chemical energy of the fuels into heat enrgy which is later on converted nto mechanical energy. | |
| 76. |
An object of mass 12 kg is at a certain height above the gorund if the potential energy of the object is 480J find the height at which the object is withj respect to the ground Given, ` g = 10m//s^2` |
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Answer» Mass of the object, `m = 12 kg`, potential energy, `E_(p) = 480 J`. `E_(p) = mgh` `480 J = 12 kg xx 10 ms^(2) xx h` `h = (480 J)/(120 kg m s^(-2))=4m` The object is at the height of 4 m. |
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| 77. |
In the shown figure, the spring and string is ideal. The spring the stiffness of `100 N//m` and `m = 1 kg` friction exists between mass 2m and surface with coefficient `mu = 0.8`. The system is released with spring from its relaxed position. Based on above data, answer the following question: (take `g = 10 m//s^(2)`) Magnitude of work done by gravity during the motion of system is :A. 0.8 JB. 1.6 JC. 0.4 JD. 4 J |
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Answer» Correct Answer - B |
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| 78. |
A lorry and a car, moving with the same kinetic energy are brought to rest by application of brakes which provied equal retarding forces. Which one of them will come to rest in a shorter distance ? |
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Answer» The kinetc energy of each vechical (the lorry and the car) is spent in doing work against the retarding force (F) of brakes, i.e., `E_k = W = F xx s or s =(E_k)/(F)` Sicne `E_k` and F are the same, s is the same in both the cases, i.e., both the lorry and the car will come to rest after coverting the some distance (s). |
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| 79. |
Find the mass of the body which has 5J of kinetic energy while moving at a speed of `2m//s.` |
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Answer» Here, kinetic energy of the body, `E_k =5J` speed of the body, `upsilon = 2m//s` if m is the mass of the body, then `E_k = (1)/(2)m upsilon^2 or m = (2E_k)/(upsilon^2) = (2xx5J)/((2m//s)^2) =2.5kg` |
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| 80. |
A rod of mass `m` and length `l` is lying on a horizontal table. Work done in making it stand on one end will beA. `mgl`B. `mgl//2`C. `mgl//4`D. `2mgl` |
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Answer» (b) Work done = final PE. - initial PE. = `mg (1//2) - 0 = mgl//2` (as when the rod is standing on one end, its centre of gravity is at a distance `1//2` from the table and when it is lying on the table, its CG is on the table, i.e., at zero distance from the table) |
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| 81. |
What quantity does the area of the graph represent ? What is the magnitude of this quantity ? |
| Answer» The are of the graph `(F xx s)` represents the work done (W) by the force in moving the body through a distance (s.) W = area of the shaded triangle `= (1)/(2) (base xx height) = (1)/(2) (0.5 m) (275 N) = 68.8 J.` | |
| 82. |
Is energy a vector quantity ? |
| Answer» Energy is not a vector quantity - it is a scalar quantity. | |
| 83. |
In Physics, energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical system. However, this must be understood as an ovberly simplified definition as we shall come to know in higher classes that not all energy can perform work. (a) How did the concept of energy emerge ? (b) How much electric energy is generated in a typical lightning strike ? What are the forms to which this energy gets converted ? (c ) What is the kinetic energy of a passenger seated in a moving plane : (i) with respect to the plance (ii) wiht respect to the Earth. |
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Answer» The concept of energy emerged out of the idea of Vis Viva (living force) and it was believed that total Vis Viva was conserved. (b ) 500 mega Joules. Light energy, sound energy, thermal energy, etc. (c ) (i) Zero (ii) Non - zero kinetic energy (and higher total energy). |
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| 84. |
Is work a scalar quantity or a vector quantity ? |
| Answer» Work is a scalar quantity. | |
| 85. |
The negative of the work done by the conserative internal forces on a system equals the change ilnA. total energyB. kinetic energyC. potential energyD. none of these |
| Answer» Correct Answer - C | |
| 86. |
The potential energy at a point, relative to the reference point is always defined as the negative of work done by the force as the object moves from the reference point to the point considered. The value of potential energy at the reference point itself can be set equal to zero because we are always concerned only with differences of potential energy between two points and the associated change of kinetic energy. A particles A is fixed at origin of a fixed coordinate system. A particle B which is free to move experiences an force `vec(F) = (-(2a)/(r^(3)) + (beta)/(r^(2))) hat(r)` due to particle A where `hat(r)` is the position vector of particle B relative to A. It is given that the force is conservative in nature and _potential energy at infinity is zero. If B has to be removed from the influence of A, energy has to be supplied for such a process. The ionization energy E 0 is work that has to be done by an external agent to move the particle from a distance `r_(0)` to infinity slowly. Here `r_(0)` is the equilibrium position of the particle Find the ionization energy `E_(0)` of the particle BA. `(beta^(2))/(2 alpha)`B. `(2 beta^(2))/(alpha)`C. `(beta^(2))/(4 alpha)`D. `(beta^(2))/(alpha)` |
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Answer» Correct Answer - C |
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| 87. |
What is the implication of negative potential energy of a body ? |
| Answer» Work has to be done to bring the body back to zero level of potential energy. | |
| 88. |
When a person does work, what determines his sence of fatigue : total work done or the rate at which he works ? |
| Answer» By the rate at which the person works. (When a man ascends a flight of steps in 20 s, he feels less fatigue then when he completes the same ascent in 4 s). | |
| 89. |
When is work done by a force zero ? |
| Answer» Work done by a force is zero if the direction of force and displacement are perpenddicular to each other or if the displacement is zero. | |
| 90. |
When gravity is the only force doing work on a body, what can we say about its energy ? |
| Answer» KE +PE = constant, i.e., total mechanical energy is conserved. | |
| 91. |
How is work done by a force meaured ? |
| Answer» Work done `(W)` = force` (F) xx` displacement (s). | |
| 92. |
When is work done by a force postivie ? |
| Answer» Work done by a force is positive if force and displacement are in the same direction. | |
| 93. |
What happens to the total energy of a star that undergoes a supernove explosion ? |
| Answer» It is conserved. | |
| 94. |
A body of mass 4kg, is taken from a height of 5 m to a hegiht 10m. Find increase in potential energy. |
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Answer» Here, mass of the body, m =4kg increase in height of the body, `h = (10m -5 m) =5m` increase in potential energy `E_p = mgh = (4kg)(10m//s^2) (5m) = 200J` Aliter. Intial potential energy of the body, `E_(pi) = mgh_i = (4kg)(10m//s^2) (5m) = 200J` final potential energy of the body, `E_(pf) mgh_f = (4kg)(10cm) = 400J` Increase in potential energy , `E_p =E_(pf) - E_(pi) =400J -200 J = 200J` |
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| 95. |
A particle mass is tied to an ideal string and whirled in a vertical circle of radius L, where L is off-course the length of the string. If the ratio of the maximum to minimum tension in the string throughout the motion is 2 : 1, then the maximum possible speed of the partcle will be:A. `sqrt(11 gL)`B. `sqrt(5 gL)`C. `sqrt(10 gL)`D. sqrt(3 gL)` |
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Answer» Correct Answer - A |
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| 96. |
What is the kinetic energy of an object ? |
| Answer» The energy of an object due to its motion is called kinetic energy. The kinetic energy of a moving object is measured by the amount of work it can do before coming to rest. | |
| 97. |
Write an expression for kinetic energy of an object. |
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Answer» Kinetic energy of an object `= (1)/(2)mv^(2)` where m = mass of the object and v = velocity of the object (or speed of the object) |
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| 98. |
How is nuclear energy converted into electrical energy ? |
| Answer» Nuclear power plants convert nuclear energy into electrical energy. | |
| 99. |
What measures the speed at which work is done ? |
| Answer» Answer:- Power. | |
| 100. |
A coolie carries a load of 50 kg on his head and walks on a level road upto 100m. What is the work done by him? |
| Answer» Word done is zero as F (load of 50kg) and s are perpendicular to each other. | |