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The correct answer is (b) Friction FORCE

Best explanation: In the PHYSICAL world, no SURFACE is frictionless. Hence whenever a body moves, the force of friction acts on it. REST all forces act on the body only when it moves ALONG a curve and not along a straight line.

Right answer is (B) Vector DIFFERENCE

Explanation: To find the relative value of any quantity, vector difference is used. The relative value is DEFINED as the subtraction of the remaining vector from the vector whose relative value is to be CALCULATED with respect to the remaining vector.

Correct ANSWER is (B) Uniformly accelerated

To ELABORATE: The three equations of motion are valid for uniformly accelerated motion. The equations do not work in situations where the acceleration is non-uniform. In that CASE it is BETTER to work with the differential forms of velocity and acceleration.

Correct answer is (b) Uniformly accelerated

The best explanation: The three equations of motion are valid for uniformly accelerated motion. The equations do not WORK in situations where the acceleration is non-uniform. In that case it is better to work with the DIFFERENTIAL FORMS of velocity and acceleration.

Correct option is (a) 2

For EXPLANATION I WOULD say: Here we will use the second equation of motion, s = ut + (1/2)at^2. Here, u = 0, s = 3600, t = 60s. On SOLVING, we will GET a = 2 m/s^2.

Right answer is (B) It is zero

Easiest EXPLANATION: The average VELOCITY is zero. The ball covers positive displacement when it goes up and negative displacement when it comes down. HENCE the TOTAL displacement is zero. Therefore, the average velocity is zero.

The CORRECT option is (b) -30 m/s

The BEST I can explain: The formula for relative velocity is VR = Vector VA – Vector VB. ASSUMING the CARS move in the same direction, the relative velocity = 20-50 = -30 m/s. The relative velocity of the second with respect to the first car is 30 m/s.

Correct answer is (a) 60

Best EXPLANATION: Acceleration of a body can be found out by differentiating the expression for VELOCITY. Here V = 5t^3. On differentiating, a = dv/dt = 15t^2. On putting t = 2, we get a = 60 UNITS.

The correct answer is (b) It is zero

The best EXPLANATION: Take any POINT on the circular path. The car moves in a CIRCLE and hence will come back to the same point after a definite time interval. Therefore, the DISPLACEMENT is 0. Hence, the AVERAGE velocity is zero.

Right OPTION is (a) A straight line with positive SLOPE

The best I can explain: As the ball falls down, its velocity increases. This is because of the acceleration due to GRAVITY. Hence the graph looks like a straight line with positive slope. The first equation of MOTION VERIFIES this.

Correct choice is (a) Linearly

To explain I would say: VELOCITY varies parabolically IMPLIES that velocity is of the FORM at + bt^2. On differentiating the velocity, we GET the equation for acceleration. THEREFORE, a = dv/dt = a+2bt, which is a linear equation. Hence the acceleration varies linearly.

Right choice is (B) 0.5

Easiest explanation: Acceleration is the RATE of change of velocity. Here, the velocity CHANGES FORM 3 m/s to 5 m/s in 5s. Hence, acceleration = (5-3)/5 = 0.4 m/s^2.

The correct answer is (C) Average speed <= INSTANTANEOUS speed

Easiest EXPLANATION: Average speed is the ratio of total distance to total time. Instantaneous speed is the ratio of instantaneous change in distance to instantaneous change in time. Average speed can be equal to instantaneous speed but is usually LESS than that.

Correct answer is (a) VECTOR VR = Vector VA – Vector VB

For explanation I would say: The relative velocity of one BODY with respect to another body can be found out by subtracting their respective velocities in respective ORDER. This rule applies not only to velocity, to all other vector QUANTITIES.

Correct answer is (a) Instantaneous velocity

The best I can explain: Instantaneous velocity describes the velocity of an object at a given TIME instant. Average speed is the speed at which the object travels throughout the time PERIOD and not an instant. Speed is a scalar QUANTITY; hence it cannot show the DIRECTION of motion.

Correct option is (a) 1.25m

Easy explanation: Here we will use the THIRD equation of motion. The third equation of motion is V^2 = U^2 + 2AS, u = 0, a = 10, v = 5. Therefore, on solving, we get s = 1.25m.

The CORRECT OPTION is (a) It increases

To explain: The instantaneous velocity will increase with TIME. If the motion is ACCELERATED, no matter if the acceleration is constant, or VARIABLE, the instantaneous velocity will increase. Variation of acceleration describes how to change in velocity is changing.

Correct CHOICE is (a) Potential energy

Explanation: When the BODY is in the state of REST, there is no motion. Hence there is no kinetic energy, hence the total energy of the body is stored as its potential energy. The total energy is the SUM of kinetic and potential energies.