A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force on it if its mass is 7 metric tonnes.

Explanation

Initial velocity, `u = 0 ms^(-1)`
Distance, s = 400 m
Time, t = 20 s
Mass, m = 7 metric tonnes = 7000 kg
By second equation of motion,
`s = u t + (1)/(2)a t^(2)`
`rArr 400 m = 0 ms^(-1) xx 20s + (1)/(2) xx a xx (20 s)^(2)`
`rArr 400 m = (1)/(2) xx a xx 400 s^(2)`
`rArr a = (400 m)/(-200 s^(2)) = 2ms^(-2)`
By Newton.s second law of motion
`F = m xx a`
`F = 7000 kg xx 2 ms^(-2)`
= 14,000 N