Forces, Movement, Shape, and Momentum
4 marks · EasyA car slows from 20 m/s to rest in 4 s when the brakes are applied. The car has a mass of 1000 kg.
Calculate the acceleration of the car while braking.
Calculate the braking force applied to the car.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) -5 m/s^2
(b) -5000 N
Common mistakes: Sign confusion (negative acceleration)
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct substitution into acceleration equation a = (v-u)/t = (0-20)/4. (follow-through)
A1 (a) · 1 mark · Correct value and unit: -5 m/s^2. (follow-through)
M2 (b) · 1 mark · Substitutes values into F = m × a with correct values from part a. (follow-through)
A2 (b) · 1 mark · Correct value and unit: -5000 N (allow sign or magnitude). (follow-through)
Worked solution
a) a = (v - u) / t = (0 - 20) / 4 = -20 / 4 = -5 m/s^2
b) F = m × a = 1000 kg × (-5 m/s^2) = -5000 N (force acts opposite motion)