IB Physics SL A.2.1 Newton’s three laws of motion

Apply Newton's laws to force pairs and resultant forces so you can explain motion changes in clear object-based terms.

Syllabus
First assessment 2025
Objective
—
Level
SL

Exam points

  • name both interacting bodies to identify a Newton's third-law pair, not two forces acting on one object
  • link a non-zero resultant force in the free-body diagram to acceleration or deceleration using F=ma
  • use the free-body diagram to infer that balanced forces mean constant velocity or rest, not zero forces

A.2.1—Newton’s three laws of motion question 1

[Maximum number: 4]

Question (a)

(a)

B3. This question is in two parts. Part 1 is about a collision. Part 2 is about electric current and resistance.
Part 1 A collision
Two identical blocks of mass 0.17 kg and length 0.050 m are travelling towards each other along a straight line through their centres as shown below. Assume that the surface is frictionless.

Figure for Question (a) — IB Physics SL

The initial distance between the centres of the blocks is 0.900 m and both blocks are moving at a speed of 0.18 m s−10.18 \mathrm{~m} \mathrm{~s}^{-1} relative to the surface.

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Question (i)

(i)

State Newton's third law of motion.

[ 1 ]

Question (ii)

(ii)

During the collision of the blocks, the magnitude of the force that block A exerts on block B is FABF_{\mathrm{AB}} and the magnitude of the force that block B exerts on block A is FBAF_{\mathrm{BA}}. On the diagram below, draw labelled arrows to represent the magnitude and direction of the forces FABF_{\mathrm{AB}} and FBAF_{\mathrm{BA}}.

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