AQA GCSE Physics (8463), Higher tier · Forces › Forces and motion › Forces and braking
Practise Stopping distance. 16 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
A driver sees a fallen tree 55 m ahead and makes an emergency stop. The car is travelling at 22 m/s. The driver’s reaction time is 0.65 s. When the brakes are applied, the car decelerates uniformly at 7.0 m/s2.
(a) Calculate the thinking distance.[2]
(b) Calculate the braking distance. Use the Physics Equations Sheet.[3]
(c) Determine whether the car stops before it reaches the tree.[1]
(d) On another day the driver is tired and has a reaction time of 1.2 s. The car travels at the same speed and decelerates at the same rate. Show that the car would not stop before reaching the tree.[3]
Show the answer and mark scheme
(a)Answer: 14.3 m
s = 22 × 0.65
14.3 (m)
(b)Answer: 34.6 m
0 − 222 = 2 × (−7.0) × s
s = 484 ÷ 14
34.6 (m)
(c)Answer: Yes: the stopping distance is 48.9 m, which is less than 55 m.
stopping distance = 48.9 m, which is less than 55 m, so the car stops (6.1 m) before the tree
(d)Answer: Thinking distance 26.4 m + braking distance 34.6 m = 61.0 m, which is more than 55 m.
thinking distance = 22 × 1.2 = 26.4 (m)
stopping distance = 26.4 + 34.6 = 61.0 (m)
61.0 m is greater than 55 m, so the car does not stop in time