2 Marks Questions

Question 12 Marks

Calculate the work done by a car against gravity in moving along a straight horizontal road. The mass of the car is 400kg and the distance moved is 2m.

Answer

$\because\ \text{WD}=\text{Fs}\cos\theta$As rhe angle between horicontal distance 2m and gravity vertically downward is 90º So WD.
$\text{WD}=\text{Fs}\cos90^\circ=0$
So work done by car aginst the gravity is zero.

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Question 22 Marks

Two bodies of unequal mass are moving in the same direction with equal kinetic energy. The two bodies are brought to rest by applying retarding force of same magnitude. How would the distance moved by them before coming to rest compare?

Answer

By work energy theorem change in KE is equal to work is equal done by body. Hence KE = WD

Hence, both bodies will travel equal displacement or distance (it does not depend on mass of bodies.)

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Question 32 Marks

Calculate the power of a crane in watts, which lifts a mass of 100kg to a height of 10 m in 20s.

Answer

According to the problem, mass = m = 100kg height = h - 10m, time interval, t = 20s Power is the rate of doing work with respect to time.$\text{Power}=\frac{\text{Work done}}{\text{time}}=\frac{\text{mgh}}{\text{t}}$
$=\frac{100\times9.8\times10}{20}$
$=5\times98=490\text{W}$

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Question 42 Marks

The average work done by a human heart while it beats once is 0.5J. Calculate the power used by heart if it beats 72 times in a minute.

Answer

According to the problem, average work done by a human heart per beat = 0.5J
Total work done during 72 beats in 1 minute
= 72 × 0.5J = 36J
Power = Work done = 36J/60s = 0.6w

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