Consider two frames of reference, S and S', the first one being fixed to the ground and the second one fixed to a train moving at 5.00 m//s with respect to the ground (figure) A block of mass 4.00 kg, initially at rest with respect to S', is acted upon by a 14.0 N force for 3.00s in the positive x direction. Neglect friction.
According to an observer in S,

Options

A. the initial kinetic energy of the block is 50J.
B. final kinetic energy 480.5J.
C. the change in kinetic energy 430.5J.
D. the work done by the force on the block is 430.5J.

Explanation

`k_(1)=(1)/(2)mv^(2)=(1)/(2)xx4xx25=50J`
`a=(14)/(4)=3.5m//s^(2)`
`s=w+(1)/(2)at^(2)=5xx3+(1)/(2)xx(7)/(2)xx9`
`=15+(63)/(4)=(123)/(4)m`
`v=u+at=5+(7)/(2)xx3=5+(21)/(2)=(31)/(2)m//s`
`k_(r)=(1)/(2)xx4xx(31xx31)/(4)=(961)/(2)=480.5J`
`w=fs=(861)/(2)=430.5J`