Forces and Motion
6 marks · NormalA car travels along a straight section of road. It accelerates from 10 m/s to 26 m/s in 4.0 s.
Calculate the acceleration of the car.
Calculate the distance travelled during the acceleration.
Explain one reason why the driver needs to allow extra stopping distance if the road is wet.
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) a = (26-10) / 4.0 = 16/4 = 4.0 m/s² m/s^2
(b) s = ((u + v)/2) × t = ((10 + 26) / 2) × 4 = (36/2) × 4 = 18 × 4 = 72 m
(c) Wet roads have less friction, so braking is less effective, and the car travels further before stopping. This increases the braking distance required.
Common mistakes: Failing to use correct initial/final speeds; Not considering friction for stopping
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correctly uses acceleration formula.
A1 (a) · 1 mark · Accurate calculation: 4.0 m/s².
M2 (b) · 1 mark · Uses correct formula for distance under constant acceleration.
A2 (b) · 1 mark · Accurate calculation: 72 m.
B1 (c) · 2 marks · Explains effect of friction in detail and links to stopping distance.
Worked solution
(a) a = (26 - 10) / 4 = 16 / 4 = 4.0 m/s²
(b) s = (u + v)/2 × t = (10 + 26)/2 × 4 = (36/2) × 4 = 18 × 4 = 72 m
(c) Wet road reduces friction, so braking force is reduced, and the car takes longer distance to stop.