A body of mass 4 kg is moving with momentum of `8 kg m s^(-1)`. A force of 0.2 N acts on it in the direction of motion of the body for 10 s. The increase in kinetic energy is

Options

A. 10 J
B. 8.5 J
C. 4.5 J
D. 4 J

Answer

C

Explanation

Momentum = mass x velocity
`p=m u=u=p/m=(8 kg ms^(-1))/(4 kg)=2 m s^(-1)`
Acceleration=`("Force")/("Mass")implies a=(0.2 N)/(4 kg)=0.05 m s^(-2)`
Distance travelled by the body in 10 s is
`d=ut + 1/2 at^2`
`=(2 m s^(-1))(10 s) +1/2xx(0.05 m s^(-2))(10 s)^2`
=20 m + 2.5 m = 22.5 m
Work done , W=Fd=(0.2 N) (22.5 m)=4.5 J
According to work-energy theorem
Increase in kinetic energy = Work done =4.5 J