8th grade forces and motion

Question 1

Two forces act on a box at right angles: 50 N east and 120 N north. What is the size of the resultant force, in N?

Answer N

Question 2

A skydiver's weight is 600 N. At this moment the air resistance is 600 N. What is happening to the skydiver's motion?

• A. speeds up
• B. falls at a constant speed
• C. slows down

Question 3

Is velocity a scalar or a vector quantity?

• A. scalar (size only)
• B. vector (size and direction)

Question 4

A force of 10 N is applied 2 m from a pivot, at right angles. What is the moment, in N m?

Answer Nm

Question 5

Newton's laws: which statement is NOT true?

• A. For every force there is an equal and opposite force on the other object.
• B. Seat belts help stop passengers continuing forward in a crash.
• C. The two forces in a Newton's third law pair act on the same object.
• D. A resultant force makes an object accelerate.

Question 6

On a seesaw, a child weighing 400 N sits 1 m from the pivot. How heavy must a second child sitting 2 m on the other side be to balance it, in N?

Answer N

Question 7

Newton's laws: which statement is true?

• A. A moving object needs a constant force to keep moving at steady speed in space.
• B. Heavier objects need less force to accelerate.
• C. A resultant force makes an object accelerate.
• D. The two forces in a Newton's third law pair act on the same object.

Question 8

A runner completes one full lap of a 400 m track. What is their displacement?

• A. 800 m
• B. 400 m
• C. 200 m
• D. 0 m

Question 9

The graph shows a walk: distance (m) against time (s). Points: (0, 0), A (10, 50), B (20, 50), C (40, 90). What was the speed from the start to A, in m/s?

Answer m/s

Question 10

Distance (m) against time (s) for a walk: (0, 0), A (20, 100), B (30, 100), C (40, 160). What was the average speed for the whole walk, in m/s? Give 2 decimal places.

Answer m/s

Question 11

A dog runs 30 m east, then 10 m west. What total distance does it run, in m?

Answer m

Question 12

Why is it easier to open a door by pushing far from the hinges?

• A. There is less friction there
• B. The door is lighter there
• C. Hinges push back
• D. A bigger distance from the pivot gives a bigger moment for the same force

Question 13

Distance (m) against time (s) for a walk: (0, 0), A (20, 80), B (40, 80), C (60, 140). In which section was the walker stationary (not moving)?

• A. from the start to A
• B. from A to B
• C. from B to C

Question 14

A car's engine provides a driving force of 1500 N forwards. Air resistance is 200 N and friction is 150 N, both backwards. What is the resultant force, in N?

Answer N

Question 15

A rocket pushes exhaust gas downwards. Why does the rocket go up?

• A. The air underneath lifts it like a balloon
• B. Gravity switches off
• C. The gas pushes the rocket upwards with an equal and opposite force
• D. The rocket becomes lighter than air

Question 16

Two forces act on a box at right angles: 16 N east and 30 N north. What is the size of the resultant force, in N?

Answer N