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

Answer

A, B, C, D

Explanation

`k_(i)=1/2m u^(2)=1/2xx4xx25=50 J`
`a=14/4=3.5 m//s^(2)`
`s=w+1/2at^(2)=5xx3+1/2xx7/2xx9=15+63/4=123/4 m`
`v=u+at=5+7/2xx3=5+21/2=31/2 m//s`
`k_(f)=1/2xx4xx(31xx31)/4=961/2=480.5` J
`w=fs=861/2=430.5` J