Year 7 Science · Unit 3 · Lesson 6
Extension · Apply Worksheet
Learning Goals
Extension · optional
Newton's Second Law sits in Stage 5 (SC5-WAM-01), beyond the Stage 4 Forces dot points this unit is built on. Nothing on this sheet is assessed as part of Year 7 Forces, so it is enrichment rather than required practice. Do it if you are interested, and skip it without losing any marks if you are not.
1. Name the two quantities that decide how much an object accelerates. For each one, say what happens to the acceleration when it increases.
Rank the trolleys
Rank the four trolleys by acceleration, from 1 (greatest) to 4 (least). No calculation is needed.
| Trolley | Mass (kg) | Pushing force (N) | Rank (1–4) |
|---|---|---|---|
| R | 20 | 20 | |
| P | 10 | 20 | |
| S | 20 | 10 | |
| Q | 10 | 40 |
2. Explain how you decided between trolleys P and R, and between trolleys R and S.
Cause and effect: off the lights
Fill the two empty boxes. Each box is caused by the one before it, and row 2 carries on from the end of row 1.
Read the data
Scenario: same force, four vehicles
An engineer works out how much speed four vehicles would gain in their first second if each had the same 2000 N net force pushing it forward.
| Vehicle | Mass (kg) | Speed gained in 1 s (km/h) |
|---|---|---|
| Motorcycle and rider | 250 | 28.8 |
| Small car | 1000 | 7.2 |
| SUV | 2000 | 3.6 |
| Loaded truck | 20 000 | 0.36 |
Source: values worked out for this worksheet, ignoring friction and drag.
3. The SUV has twice the mass of the small car. Use Table 1 to test the rule “double the mass, half the acceleration”.
4. Describe the overall pattern in Table 1, and use the idea of inertia to explain why it happens.
5. A family car is driven empty to the airport, and then back with five passengers and their luggage. Explain how the car’s acceleration changes on the way back if the driver presses the accelerator (a) the same amount as before, and (b) much harder. Use force, mass and acceleration.
Question 1
Force: more force, more acceleration (1). Mass: more mass, less acceleration (1). [2 marks]
Rank the trolleys
R 3, P 2, S 4, Q 1 (Q greatest, then P, R, S). All four = 2; two correct = 1. [2 marks]
Question 2
P and R: same force, P has half the mass, so more acceleration (1). R and S: same mass, R has double the force, so more acceleration (1). [2 marks]
Cause and effect: off the lights
Box 1: the truck has far more mass, so more inertia (1). Box 2: the same force on the motorcycle’s smaller mass gives it a bigger acceleration (1). [2 marks]
Read the data: Question 3
Small car 7.2 km/h, SUV 3.6 km/h (1); 3.6 is exactly half of 7.2, so the rule holds for the same force (1). [2 marks]
Question 4
More mass, less speed gained: 28.8 km/h for the motorcycle down to 0.36 km/h for the truck (1). More mass means more inertia, more resistance to a change in motion, so the same force changes it less (1). [2 marks]
Question 5
Marking guide: (a) 1 the mass increases; 1 the engine force is about the same; 1 so the acceleration is smaller. (b) 1 the force is bigger; 1 so the acceleration increases again and can match the empty car; 1 both force and mass decide the acceleration, so neither alone predicts it. [6 marks]
Model answer: (a) The passengers and luggage add mass, but the engine force is the same, so the car accelerates less. (b) Pressing harder gives a bigger force, so the acceleration rises and can match the empty car’s. Acceleration depends on both force and mass.
Common error: saying a heavy object always accelerates less, even when the force is bigger.