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AP · AP 1 · multiple choice

AP Physics 1: Algebra-Based · Question 4

AP Physics 1: Algebra-Based · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
demanding
Marks
1
Topics
1
Answer
Complete
Two balls approaching each other on a straight horizontal trackjust before the collision0.50 kg1.5 kg4.0 m/s2.0 m/s
Fig. 4.1Two balls of equal size rest on a straight horizontal track, well apart from one another. The left-hand ball is labelled 0.50 kg and carries a horizontal arrow drawn from its centre pointing to the right, labelled 4.0 m/s. The right-hand ball is labelled 1.5 kg and carries a horizontal arrow drawn from its centre pointing to the left, labelled 2.0 m/s, so the two arrows point towards each other along the same line. A note on the figure states that this is the instant just before the collision.
multiple choice1 mark

A 0.50 kg ball moving at 4.0 m/s to the right collides head-on with a 1.5 kg ball moving at 2.0 m/s to the left. The two balls stick together. What is the velocity of the combined object immediately after the collision?

  1. A

    0.50 m/s to the left

  2. B

    0.50 m/s to the right

  3. C

    2.5 m/s to the left

  4. D

    2.5 m/s to the right

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Answer overviewCorrect answer: A — 0.50 m/s to the left
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is A: 0.50 m/s to the left

  2. 2

    Total momentum is (0.50)(+4.0) + (1.5)(−2.0) = −1.0 kg·m/s, and the combined mass is 2.0 kg. B gets the size right and the sign wrong, which on a real exam is a wrong answer, not a near miss.

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