Home · IGCSE 0625 · Motion, forces, energy · Resultant forces · Practice
Practice questions · Resultant forces

Add them up.

Six original Cambridge-style questions on the effects of forces, combining forces in a line, balanced versus unbalanced, and the constant-speed-needs-no-resultant trap.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
The decision to make

Is the resultant zero, or not?

01
Analysis
[3 marks]

State three different effects that a force can have on an object.

  • Change its shape (stretch, compress or bend it). ✓
  • Change its speed (speed it up or slow it down). ✓
  • Change its direction of motion. ✓
02
Calculation
[2 marks]

Two forces act on an object along the same line: 30 N and 20 N.

(a)Find the resultant when they act in the same direction. (b)Find the resultant when they act in opposite directions.
  • (a) 30 + 20 = 50 N (in that direction). ✓
  • (b) 30 − 20 = 10 N (in the direction of the 30 N force). ✓
03
Analysis
[3 marks]

A box is pushed across the floor with a force of 40 N and moves at a constant velocity. State the size of the friction force, the resultant force, and explain how you know.

  • Friction = 40 N. ✓
  • Resultant force = 0 N. ✓
  • Constant velocity means no acceleration, so the forces are balanced; friction must equal the push. ✓
04
Analysis
[2 marks]

A car travels down a hill at a steady speed. A student says, "It is moving, so there must be a resultant force acting on it." Explain why the student is wrong.

  • Steady speed means constant velocity, which means no acceleration. ✓
  • So the forces are balanced and the resultant force is zero; a resultant is needed only to change the motion, not to maintain it. ✓
05
Calculation
[2 marks]

A van has a forward driving force of 5000 N and a total resistive force of 3500 N. Calculate the resultant force and state the effect on the van's motion.

resultant = 5000 − 3500 = 1500 N (forward)

1500 N forward

  • The van accelerates (speeds up) in the forward direction. ✓
06
Analysis
[2 marks]

An object rests on a table with balanced forces acting on it. One of the horizontal forces is then removed. Describe what happens to the object's motion and why.

  • There is now a non-zero resultant force (the remaining force is unopposed). ✓
  • The object accelerates in the direction of that remaining force. ✓