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Que.  A body of mass 5kg is moving with a momentum of 10kgm/s . A force of 0.2N acts on it in the direction of motion of the body for  10 sec. The increase in kinetic energy is

1. 2.8J         b) 4.4J     c) 3.2J d) 3.8J

Solution with Explanation : 

Here we have, 

Initial momentum of the body = 10kgm/s

mu = 10

Mass of the body = 5 kg

5u = 10

u = 10/5

u = 2 m/s

Now, the finale velocity of the body after a force of 0.2N is applied for 10 seconds

F = 0.2N               [F = ma]

ma = 0.2N            [m= 5kg and a = (v-u)/t]

5(v - u)/t = 0.2       [u = 2m/s and time(t) = 10 sec]

5(v-2) =  0.2×10

5v-10 = 2

5v = 2+10

5v = 12

v = 12/5ms-1

So the increase in kinetic energy is = ½m( v²-u²)

1/2  × 5 (144/25-4)

= 22/5

= 4.4J

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