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1.

How can you increase the mechanical advantage of a see-saw without their changing its length?

Answer» By increasing the effort arm we can increase the MA of a see-saw as it is a first order lever.
Discussion
2.

Find the mechanical advantage of the below figure:

Answer» Correct Answer - 2
`MA=(L)/(E)=(2E)/(E)=2`
Discussion
3.

A nut is placed in a nut cracker at 5 cm from the fixed end. If the force experienced by the nut is 100 N when a force of 20 N is applied at the free end of the nut cracker, find the length of the nut cracker.A. 5B. 25C. 15D. 20

Answer» Correct Answer - B
Mechanical advantage `=("Load")/("Effort")=("Effort arm")/("Load arm")`
Therefore, `(100)/(20)=("Effort arm")/(5)`
`implies` Effort arm =25 cm
Hence, the correct options is (b).
Discussion
4.

To open the lid of bottle, 50 N force is needed, Siri wanted to open the lid with her maximum effort of 10 N, which of the following openers is suitable for doing it?

Answer» Correct Answer - `E_(A)=10N,E_(B)=12.5N,E_(C)=10 N,` Either A or C.
`M_(A)=(10)/(2)=5`
`M_(B)=(8)/(2)=4`
`M_(C)=(15)/(3)=5`
`E_(A)=(L)/(MA)=(50)/(5)=10N`
`E_(B)=(L)/(MA)=(50)/(4)=12.5N`
`E_(C)=(L)/(MA)=(50)/(5)=10N`
She can use opener A or C to open the lid.
Discussion
5.

Hari is studying in 6th standard and is interested in science related experiments. While reading simple machines topic from his text book,he started wondering as to which lever a pen belongs to in its writing position? The length of the pen he is using is 14 cm and he holds it at distance of 4 cm from its nib. If the force applied by Hari to write is 0.02 N, the mechanical advantage of the pen is _____ and it is acting as a _____order lever.A. 5, secondB. 0.25, firstC. 2.5, thirdD. 0.243, third

Answer» Correct Answer - D
A pen acts as a third order lever in writing position (since the effort is applied at the middle of the fulcrum and the load).
The length of pen=load arm=14 cm
Effort arm 10=cm
Mechanical advantage of pen `=("effort arm")/("loada arm")`
`=(10)/(14)=0.243`
Hence, the correct option is (d).
Discussion
6.

Which of the following machines is used only to change the direction of input force?A. Inclined planeB. Single-fixed pulleyC. ScissorsD. Screw jack

Answer» Correct Answer - B
Single fixed pulley is used to reverse the direction of application of force.
Discussion
7.

which of the following is wrong?A. `I^(st)` order lever `:MAgt1`B. `II^(nd)` order lever `:MAgt1`C. `III^(rd)` order lever `:MAgt1`D. single-fixed pullery `:MA=1`

Answer» Correct Answer - C
In case III order lever always the load arm will be greater than the effort arm. Mechanical advantage is inversely propotional to the load arm therefore it will be always less than 1.
Discussion
8.

Which of the following planes cannot be used to push load to a certain height?A. A plane of slope 2B. A plane of slope `oo`C. A plane of slope 0D. Both (b) and (c)

Answer» Correct Answer - D
Inclined plane of zero inclination is just a horizontal surface which do not bring any change in the effort requried to do a work. Slope Infinity means the body has to be lifted to zero height i.e there is no requiremnt of an inclined plane. Therefore incilined planes of slope infinity or zero cannot be used.
Discussion
9.

What is the efficiency of a simple machine?

Answer» The efficiency of a simple machine is always less than 100%.
Discussion
10.

Which of these is not a wheel and axle?A. Screw driverB. TapC. ScrewD. Door knobs

Answer» Correct Answer - C
To understand this imagine cutting a paper diagonally and mark the inclined edge with a sketch and roll it overa pencil. It looks like a threaded screw. Similary ghat roads are made cuved along the height of the hill. Hence ghat roads can be compared to inclined plane.
Discussion
11.

Regular oiling of parts increases theirA. Output workB. EfficiencyC. Mechanical advantageD. None of these

Answer» Correct Answer - B
Oiling the machinery reduces friction and so there will be less energy lost. Hence the ouput work also increases and so the efficiency of the machine increases.
Discussion
12.

`{:("Across",|,"Down"),(1."Pulley whose axis of rotation is not fixed (2 Words)",|,1."Greater the _____ the smaler the effort required to overcome a certain load. (2 Words)"),(4."This is a second-order lever used for a fruit cutter",|,2."Inclined plane wound around"),(7."Greater the number of pullcys, _____ is the force needed to lift heavy loads".,|,3."Block and tackle means more number of ____"),(10."Scissors are an example of ____ (3 Words)",|,"5. This simple machine changes the direction of applied force"),(,|,6."This simple machine changes the direction of applied force"),(,|,8."Leading edege shape of a speed boat"),(,|,9."Tap works on the principle of_____):}`

Answer» `{:("Across",|,"Down"),(1."Movable pulley",|,1."Mechanical advantage"),(4."Mango cutter",|,2."Screw"),(7."Lesser",|,3."Pulleys"),(10."First order lever",|,5."Pulley"),(,|,6."Crowbar"),(,|,8."Wedge"),(,|,9."Screw"):}`
Discussion
13.

Write a short note on maintenance of machinery.

Answer» (a) A machine should be protected form rust by applying paint or rust-proof coating.
(b) Regular oiling of parts increases their efficiency, otherwise they wera out or make too much of noise due to friction.
(c) Machines, when not in use, should be kept covered to protect them from dust.
Discussion
14.

A crowbar of length 1 m is used to dispace a body. Find its mechanical advantage, if the load arm is 0.25 m.

Answer» Correct Answer - 3
`MA=("Effort arm")/("Load arm")`
`=(0.75)/(0.25)`
=3
MA=3
Discussion
15.

Krishna had parked his two-wheeler at 'no parking' place as he did not find any board regarding the notice NO PARKING. After some time, the traffic police took away his bike to a nearby police station, by lifting it with a rope attached to a pulley arrangement. If the mass of the bike is 150 kg, the what is its weight in dynes?A. `15xx10^(7)` dynesB. 1500 dynesC. 150 dynesD. 15 dynes

Answer» Correct Answer - A
Weight = mg
`mg=150xx10=1500N=15xx10^(7)` dynes
Hence, the correct option is (a).
Discussion
16.

If an inclined plane of length 2 m is used to lift a load of 20 N to a height of 1 m, find the effort required to lift the load to that heiht using inclined plane.

Answer» Correct Answer - 10 N
`MA=(l)/(h)=(2)/(1)=2`
`MA=(L)/(E)`
`E=(L)/(MA)=(20)/(2)=10` Effort =10 N
Discussion