Forces and Motion Quiz

Grade 8 · Science · Quiz

10 questions covering speed, velocity, acceleration, friction, gravity, and balanced vs. unbalanced forces.

Questions

1. What is the difference between speed and velocity?

   1. Velocity is faster than speed
   2. Velocity includes direction; speed does not
   3. Speed includes direction; velocity does not
   4. They are identical
   Show answer

   Answer: Velocity includes direction; speed does not

   Speed is a scalar (magnitude only); velocity is a vector (magnitude + direction). 60 km/h is speed; 60 km/h north is velocity.

2. A sprinter accelerates from 0 m/s to 10 m/s in 2 seconds. What is the acceleration?

   1. 20 m/s²
   2. 5 m/s²
   3. 0.2 m/s²
   4. 12 m/s²
   Show answer

   Answer: 5 m/s²

   a = (v_f − v_i) ÷ t = (10 − 0) ÷ 2 = 5 m/s².

3. Friction always acts in the same direction as the motion of an object.

   Show answer

   Friction opposes motion — it acts in the direction opposite to the object's movement.

4. A book sits on a desk without moving. The forces acting on it are:

   1. Unbalanced — gravity is stronger
   2. Balanced — gravity and normal force are equal and opposite
   3. There are no forces on the book
   4. Only the normal force acts on it
   Show answer

   Answer: Balanced — gravity and normal force are equal and opposite

   The book is in equilibrium — gravity pulls down, the desk's normal force pushes up with equal magnitude. Net force = 0.

5. An object moving in a circle at constant speed is:

   1. Not accelerating because speed is constant
   2. Accelerating because its direction is constantly changing
   3. Experiencing balanced forces
   4. Moving with constant velocity
   Show answer

   Answer: Accelerating because its direction is constantly changing

   Acceleration is any change in velocity. Since velocity includes direction, changing direction means changing velocity — so circular motion involves constant acceleration toward the center.

6. A force that opposes the motion of surfaces sliding against each other is called ___.

   Show answer

   Friction converts kinetic energy to thermal energy (heat) and slows moving objects.

7. On a distance-time graph, a straight horizontal line indicates:

   1. The object is accelerating
   2. The object is moving at constant speed
   3. The object is not moving
   4. The object is decelerating
   Show answer

   Answer: The object is not moving

   A horizontal line on a distance-time graph means distance is not changing over time — the object is stationary.

8. A net force of zero means an object must be at rest.

   Show answer

   Zero net force means no acceleration. An object can be moving at constant velocity and still have zero net force — it doesn't have to be at rest.

9. Which of the following is NOT an example of acceleration?

   1. A car speeding up
   2. A ball slowing down after being thrown
   3. A car turning a corner at constant speed
   4. A train moving at constant speed in a straight line
   Show answer

   Answer: A train moving at constant speed in a straight line

   Constant speed in a straight line means constant velocity — no change in speed or direction, therefore no acceleration.

10. A bicycle rider travels 30 meters in 5 seconds. What is the average speed?

    1. 150 m/s
    2. 25 m/s
    3. 6 m/s
    4. 0.17 m/s
    Show answer

    Answer: 6 m/s

    Speed = distance ÷ time = 30 m ÷ 5 s = 6 m/s.

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