Newton’s laws test answers and mark scheme for grade 8 science (free PDF download)

Question 1 First law and inertia (2 marks)

1. An object stays at rest or moves at constant velocity unless an unbalanced force acts on it.
2. The tendency of an object to resist a change in its motion (greater for greater mass).

Marking: 1 mark each.

Question 2 Crate on a floor (3 marks)

1. 60 − 24 = 36 N to the right.
2. a = F ÷ m = 36 ÷ 12 = 3.0 m/s².

Marking: Part a: 1 mark. Part b: 1 mark for the formula and substitution, 1 mark for 3.0 m/s².

Question 3 Cricket ball (3 marks)

1. F = m × a = 0.15 × 400 = 60 N.
2. a = 60 ÷ 0.30 = 200 m/s² (half as much).

Marking: Part a: 1 mark for the formula, 1 mark for 60 N. Part b: 1 mark.

Question 4 Rocket (3 marks)

1. When A exerts a force on B, B exerts an equal and opposite force on A.
2. The gas pushes the rocket upward.
3. The upward force of the gas on the rocket is bigger than the rocket’s weight, so there is an unbalanced upward force.

Marking: 1 mark per part.

Question 5 Passengers in a car (3 marks)

1. Newton’s first law (inertia).
2. The bag keeps moving at the car’s original speed, because there is no unbalanced force on it, while the seat and car slow down; so the bag slides forward relative to the seat.

Marking: Part a: 1 mark. Part b: 1 mark for no force on the bag, 1 mark for continuing at its original velocity.

Question 6 Speeding up a car (3 marks)

1. a = 2500 ÷ 1000 = 2.5 m/s².
2. Speed = 2.5 × 6.0 = 15 m/s.

Marking: Part a: 1 mark. Part b: 1 mark for the method, 1 mark for 15 m/s.

Question 7 Mass and weight (2 marks)

1. It is still 8.0 kg; mass does not change with location.
2. W = m × g = 8.0 × 9.8 = 78.4 N.

Marking: 1 mark each.

Question 8 Do they cancel? (1 mark)

Marking: 1 mark for stating they act on different objects.