A body of mass `0.4kg` starting at origin at `t=0` with a speed of `10ms^(-1)` in the positive x-axis direction is subjected to a constant `F=8` N towards negative x-axis. The position of body after 25s is

Options

A. `-6000 m`
B. `-8000 m`
C. `+4000 m`
D. `+7000 m`

Answer

A

Explanation

`m = 0.4 kg : u = 10 m//s : a = (-F)/(m) = (-8)/(0.4) = - 20m//s^(2)`
Position of particle at any time
`x = x_(0) + ut + (1)/(2) at^(2)`
`t = 0, x_(0) =0`
`x = ut + (1)/(2)at^(2)`
`rArr x = 10 xx 25 + (1)/(2) (-20)(25)^(2)`
`x = - 6000 m`.