AQA AS Level Physics Paper 2, November 2021: Question 24

1 mark · Medium difficulty · Multiple Choice

Determine the motion of a lift given that a suitcase of weight 200 N registers a reading of 180 N on a weighing scale inside it.

Practise this question

Question

Multiple choice question 24 asking to identify the motion of a lift based on a 200 N suitcase reading 180 N on a scale. Four options are provided: A, moving down at a constant velocity; B, moving down with a decreasing velocity; C, moving up at a constant velocity; D, moving up with a decreasing velocity.
Question text

24 A suitcase weighing 200 N is placed on a weighing scale in a lift.

The scale reads 180 N when the lift is moving.

The lift is

[1 mark]

A moving down at a constant velocity.

B moving down with a decreasing velocity.

C moving up at a constant velocity.

D moving up with a decreasing velocity.

Mark scheme

Show the mark scheme Mark scheme showing the correct answer for question 24 is D, corresponding to moving up with a decreasing velocity.

24 D moving up with a decreasing velocity.

How to answer it

Lift Forces & Apparent Weight (Question 2.4)

What this question tests

This question assesses your understanding of Newton's laws of motion, specifically how apparent weight measured by a scale changes during vertical acceleration and deceleration, and how to link the normal contact force to the direction of motion and velocity changes.

Question Part 2.4

Multiple Choice Analysis

✅ Correct Answer: D

Moving up with a decreasing velocity.

The scale reading (normal contact force) is 180 N , which is less than the actual weight of the suitcase ( 200 N ). This means there is a resultant force acting downwards. A downward resultant force while moving upwards means the lift is decelerating (decreasing velocity).

💡 Key Knowledge

  • Scale Reading = Normal Contact Force (R): The reading on a weighing scale in a lift shows the upward reaction force exerted by the scale on the object.
  • Weight (W): Pull of gravity acting downwards ( W = mg ).
  • Newton's Second Law: F_net = W - R = ma (taking downward as positive when W > R ).

🧠 Exam Technique

  • Compare the scale reading to the real weight immediately: 180 N < 200 N .
  • Deduce the direction of the resultant force: Since the scale reads less, the resultant force must be downwards.
  • Eliminate options: Constant velocity (A and C) requires R = W (scale reading = 200 N). Therefore, A and C are incorrect.
  • Link direction of motion to deceleration: To have a downward force while moving up (D), the lift must be slowing down (decreasing velocity). Moving down with decreasing velocity (B) would require an upward resultant force ( R > W ).

❌ Common Errors

  • Assuming that a lower scale reading automatically means the lift is moving downwards. Direction of motion and direction of acceleration/resultant force are independent!
  • Confusing increasing and decreasing velocity when matching acceleration direction to motion direction.
Mark Allocation: [1 mark] awarded for selecting option D.

Topics

Physics · 3.4 Mechanics and materials

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.