What does this fourth paper cover?

Momentum p = mv, weight on the Earth and on the Moon, reaction distance, total stopping distance, conservation of momentum in a perfectly inelastic collision, net force with friction, free fall and scale readings in a lift.

Why is the stopping distance split into two parts?

During the reaction time the car has not braked and still moves at constant speed, so that distance is v x t; only the braking stage uses the deceleration formulas.

S4 Physics Force and Motion Practice Paper (Set 4): 10 Questions with Answers on Stopping Distance, Conservation of Momentum and Action-Reaction Forces

2026-11-01

Tutor Prep Guide · Secondary Physics

The fourth force and motion paper drills total stopping distance from reaction plus braking, momentum conservation in collisions, net force with friction, lift scale readings and action-reaction pairs, each with an answer and a one-line explanation.

Direct answers This paper has 10 questions, from momentum and Newton’s laws to stopping distance and scale readings, with g = 10 m/s^2 and 1.6 m/s^2 for the Moon; suggested time is 25 minutes.

01 Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25 minutes
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	S4 Physics: Force and Motion
Level	S4 (DSE)

02 Questions (10 items)

FoundationA 5 kg ball moves at 6 m/s. What is its momentum?
FoundationWhat is the weight of a 20 kg instrument on the Earth and on the Moon? (Moon g = 1.6 m/s^2)
FoundationA body accelerates uniformly from 6 m/s to 14 m/s in 4 s. What is its acceleration?
FoundationA car travels at 15 m/s and the driver’s reaction time is 0.8 s. How long is the reaction distance?
IntermediateA car travels at 20 m/s, the driver reacts in 0.5 s, and the car then decelerates uniformly at 5 m/s^2 to a stop. What is the total stopping distance?
IntermediateA 2 kg ball moving at 6 m/s hits a stationary 4 kg ball and they stick together. What is their common velocity?
IntermediateA 10 kg crate on a horizontal floor is pulled with 40 N while friction is 15 N. What is its velocity 5 s after starting from rest?
ChallengeA stone falls freely from the roof of a 45 m building (g = 10 m/s^2, air resistance neglected). How long does it take to land, and at what velocity?
ChallengeA 60 kg person stands on a scale inside a lift accelerating upwards at 2 m/s^2. What does the scale read?
Error redoCar A of 20 kg and car B of 30 kg collide. A exerts 60 N on B. How much force does B exert on A? (Common wrong answers are 90 N and 40 N.)

03 Answers and one-line notes

#	Answer	One-line note
1	p = m x v = 5 x 6 = 30 kg m/s.	Momentum is mass times velocity and points the same way as the velocity.
2	On Earth W = 20 x 10 = 200 N; on the Moon W = 20 x 1.6 = 32 N.	Mass is the same everywhere; weight changes with the gravitational acceleration.
3	a = (14 – 6) / 4 = 2 metres per second squared.	Acceleration is the change in velocity divided by the time.
4	Reaction distance = 15 x 0.8 = 12 m.	The car does not slow down during the reaction time, so it keeps moving at its original speed.
5	Reaction distance = 20 x 0.5 = 10 m; braking distance = 20 squared / (2 x 5) = 40 m; total 50 m.	Stopping distance = reaction distance + braking distance, and the two stages cannot share one formula.
6	Conservation of momentum: 2 x 6 = (2 + 4) x v, so v = 12 / 6 = 2 m/s.	Sticking together is a perfectly inelastic collision: momentum is conserved but kinetic energy is not.
7	Net force = 40 – 15 = 25 N; a = 25 / 10 = 2.5 metres per second squared; v = 2.5 x 5 = 12.5 m/s.	Find the net force and then the acceleration; never divide the pull by the mass directly.
8	s = half g t squared, so 45 = 5 t squared and t = 3 s; v = gt = 30 m/s.	A freely falling body starts from rest, so the displacement depends only on the square of the time.
9	N = m(g + a) = 60 x (10 + 2) = 720 N (equivalent to a 72 kg weight).	The normal force must exceed the weight when the lift accelerates upwards, so the reading is heavier than at rest.
10	Also 60 N, in the opposite direction.	Newton’s third law: action and reaction are equal in magnitude, whatever the ratio of the two masses.

04 What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Separate the reaction stage from the braking stage in every stopping-distance question, then check your two stages against the answer.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.