Question

A 1000 kg vehicle moving with a speed of 20 m/s is brought to rest in a distance of 50 metres :
(i) Find the acceleration.
(ii) Calculate the unbalanced force acting on the vehicle.

Answer 1

(i) Final velocity, v = 0 (because the car is brought to rest)
Distance covered, s = 50 m
So, Force = mass × acceleration
But we do not know the value of a.
Making use of the third equation of motion we get,
v² − u² = 2as
⇒ 0 − 20² = 2 × a × 50
⇒ −400 = 100a
⇒ a = −4
The acceleration = −4 m/s²

(ii) Force = mass × acceleration
Mass = 1000 kg
Force  = 1000 × (−4)
           = − 4000 N
Unbalanced force acting on the vehicle is −4000 N.