The force exerts a deceleration on the body and it can be found by,
`F = ma`
`50 = 20 xx a`
`a = 2.5 ms^(-2)`
The deceleration is `2.5 ms^(-2).`
To find the time taken to stop the mass, we can use, v = u+at
`0 = 15 -2.5t`
`t = 15/2.5`
`t = 6 s.`
Therefore, it would take 6 seconds to stop the mass.
Given that: m=20kg., mass of body
u=15m/s, initial velocity
F=50N,force of retardation
the deceleration act on the body can be found by Newton's second law as:
=>a=5/2 m/s2 (deceleration)
from third equation of motion,under retardation :v2=u2-2as
body will move 45m before being to stop.
from first equation of motion: v=u-at(a is negative,for retardation)
body will take 6sec.to come to stop.
Hope,you will be satisfied.