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Q.

How much work should be done on a bicycle of mass 20 kg to increase its speed from 2 ms-1 to 5 ms-1? (Ignore air resistance and friction).


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a

170 J

b

210 J

c

270 J

d

330 J 

answer is B.

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Detailed Solution

The work done should be 210 J to increase the speed from 2 ms-1 to 5 ms-1.
Given data:
Mass of bicycle, = 20 kg
Initial speed of the bicycle, u=2 ms-1
Final speed of the bicycle,  v=5 ms-1
To find the work done:
We know that whenever work is done, an equal amount of energy is used up.
According to the work-energy theorem, the work done in this case will be equal to the change in kinetic energy of the bicycle when its speed changes from 2 ms-1 to 5 ms-1.
Mathematically express:
Work done=Final K.E-Initial K.E
           =12mv2-12mu2
          =12×20×52-12×20×22
          =250-40
          =210 J
Hence, the work done is 210 J.
 
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