8th grade forces and motion

Question 1

Two forces act on a box at right angles: 120 N east and 160 N north. What is the size of the resultant force, in N?

Answer N

Question 2

Newton's laws: which statement is true?

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

Question 3

Newton's laws: which statement is NOT true?

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

Question 4

Distance (m) against time (s) for a walk: (0, 0), A (10, 50), B (20, 50), C (30, 80). 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 5

The graph shows a walk: distance (m) against time (s). Points: (0, 0), A (10, 50), B (30, 50), C (50, 110). What was the speed from the start to A, in m/s?

Answer m/s

Question 6

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

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

Question 7

A dog runs 20 m east, then 30 m west. What total distance does it run, in m?

Answer m

Question 8

Distance (m) against time (s) for a walk: (0, 0), A (20, 60), B (40, 60), C (50, 120). What was the average speed for the whole walk, in m/s? Give 2 decimal places.

Answer m/s

Question 9

A car's engine provides a driving force of 1200 N forwards. Air resistance is 200 N and friction is 150 N, both backwards. What is the resultant force, in N?

Answer N

Question 10

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 11

The same force is applied to an empty trolley and a full one. Which accelerates more?

• A. neither moves
• B. both the same
• C. the full trolley
• D. the empty trolley

Question 12

On a seesaw, a child weighing 400 N sits 2 m from the pivot. How heavy must a second child sitting 3 m on the other side be to balance it, in N?

Answer N

Question 13

A force of 25 N is applied 2 m from a pivot, at right angles. What is the moment, in N m?

Answer Nm

Question 14

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

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

Question 15

Is weight a scalar or a vector quantity?

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

Question 16

Two forces act on a box at right angles: 15 N east and 20 N north. What is the size of the resultant force, in N?

Answer N