Science 8 · Unit 3: Forces and energy · Cambridge Lower Secondary Science Stage 8

Questions

1. 1. What is needed for two forces to be balanced?

   • They must act in the same direction.
   • One must be zero.
   • They must be the same size and in opposite directions.
   • They must be different sizes.
   Check

2. 2. A box sits on the ground, not moving. Which is true?

   • An unbalanced force acts on it.
   • Balanced forces act on it.
   • Only gravity acts on it.
   • No forces act on it.
   Check

3. 3. What happens to an object when the forces on it are balanced?

   • It always stops.
   • It changes direction.
   • It always speeds up.
   • It stays still or keeps moving at a constant speed.
   Check

4. 4. Which can happen because of unbalanced forces?

   • A car moves at a constant speed.
   • A boat floats at rest.
   • A football changes direction.
   • A book stays still on a desk.
   Check

5. 5. A car's driving force is larger than friction. What happens?

   • The car stops.
   • The car speeds up.
   • The car stays at the same speed.
   • The car slows down.
   Check

6. 6. A boat's engine stops. Water resistance is now unbalanced. What happens?

   • The boat slows down.
   • It speeds up.
   • It sinks.
   • It keeps the same speed.
   Check

7. 7. Sofia's driving force on her bicycle equals friction. What is her motion?

   • turning
   • speeding up
   • constant speed
   • slowing down
   Check

8. 8. A plane flying north must turn east. Which way must the unbalanced force act?

   • towards the south
   • towards the north
   • towards the east
   • towards the west
   Check

9. 9. A tennis ball on a string moves in a circle round a pole. Which way does the unbalanced force act?

   • towards the pole (the centre)
   • away from the pole
   • in the direction of motion
   • straight down
   Check

10. 10. The string breaks. Which way does the ball move?

    • in a circle
    • in a straight line in the direction it was moving
    • directly away from the pole
    • towards the pole
    Check

11. 11. How can a flying bird go higher?

    • increase the upward lift force
    • increase drag
    • increase its weight
    • stop flapping
    Check

12. 12. How can a flying bird slow down?

    • reduce its weight
    • increase thrust
    • reduce drag
    • reduce its thrust or increase drag
    Check

13. 13. What is the resultant force when 10 N pushes right and 10 N pushes left?

    • 10 N
    • 5 N
    • 20 N
    • 0 N
    Check

14. 14. What is the resultant force when 15 N pushes right and 5 N pushes left?

    • 10 N to the right
    • 10 N to the left
    • 20 N to the right
    • 0 N
    Check

15. 15. Can an object be moving if the forces on it are balanced?

    • Only if it is falling.
    • Yes, at a constant speed in a straight line.
    • Only if it is speeding up.
    • No, never.
    Check

16. 16. Which of these has balanced forces acting on it?

    • a girl on a swing getting faster
    • a bowling ball rolling at constant speed in a straight line
    • a motorcycle going around a corner
    • a coconut falling and getting faster
    Check

17. 17. A parachute opens while an object is falling fast. Why does the object slow down?

    • The forces are balanced.
    • Gravity stops acting.
    • Its weight gets bigger.
    • Air resistance is bigger than its weight.
    Check

18. 18. In a tug of war, both teams pull but the rope does not move. Why?

    • Friction stops the rope.
    • The rope has no weight.
    • The teams pull with equal forces in opposite directions.
    • Neither team is pulling.
    Check