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

Answer

A

Explanation

Here, Mass of the particle, m=0.4kg
`F=-8N` (minus sign for direction of force)
`therefore "Acceleration", a=(F)/(m)=(-8N)/(0.4kg)=-20ms^(-2)`
The position of the body at any time t is given by
`x=x_(0)+ut+(1)/(2)at^(2)`
The position of the body at t=0 is 0, therefore `x_(o)=0` `therefore x=ut+(1)/(2)at^(2)`
Position of the body at t=25s
Here, `u=1-x25+(1)/(2)(-20)(25)^(2)=250-6250=6000m`