8th Grade Science Study Guide: Speed, Velocity, and Acceleration Concept Review Questions

1. Define speed and how it differs from velocity.
   
   

   • Speed is the rate at which an object moves, calculated as distance divided by time.

   • Velocity includes both speed and direction.

2. What is acceleration, and how is it calculated?
   
   

   • Acceleration is the rate of change of velocity over time.

   • Formula: a = Δv / Δt, where Δv is the change in velocity and Δt is the change in time.

3. What is the SI unit for speed, velocity, and acceleration?
   
   

   • Speed and velocity: meters per second (m/s)

   • Acceleration: meters per second squared (m/s²)

4. Explain the difference between positive and negative acceleration.
   
   

   • Positive acceleration: Object is speeding up.

   • Negative acceleration (deceleration): Object is slowing down.

5. What is the difference between instantaneous speed and average speed?
   
   

   • Instantaneous speed: Speed of an object at a specific moment.

   • Average speed: Total distance traveled divided by total time taken.

6. How does direction affect velocity?
   
   

   • Velocity includes direction, so a change in direction changes velocity, even if speed remains the same.

7. Describe a situation where an object can have constant speed but changing velocity.
   
   

   • An object moving in a circular path (e.g., a car on a roundabout) has constant speed but changing velocity due to direction change.

8. If a car is moving at a constant velocity, what is its acceleration?
   
   

   • Zero, because there is no change in velocity.

9. Explain how a distance-time graph can be used to determine speed.
   
   

   • The slope of the line represents speed; a steeper slope means a higher speed.

10. Explain how a velocity-time graph can be used to determine acceleration.
    
    

    • The slope of the velocity-time graph represents acceleration; a positive slope means speeding up, and a negative slope means slowing down.

Practice Problems

11. A person walks 10 meters north, then 5 meters south. What is their total distance traveled and their displacement?
    
    

    • Total distance: 10 m + 5 m = 15 m

    • Displacement: 10 m north - 5 m south = 5 m north

12. A car travels 120 km in 2 hours. What is its average speed in km/h?
    
    

    • v = 120 ÷ 2 = 60 km/h

13. Convert 36 km/h to meters per second.
    
    

    • 36 × (1000 ÷ 3600) = 10 m/s

14. A plane travels at a speed of 250 m/s. Convert this speed to km/h.
    
    

    • 250 × (3600 ÷ 1000) = 900 km/h

15. A cyclist accelerates from 5 m/s to 15 m/s in 4 seconds. What is the acceleration?
    
    

    • a = (15 - 5) ÷ 4 = 2.5 m/s²

16. A car moving at 20 m/s comes to a stop in 5 seconds. What is its acceleration?
    
    

    • a = (0 - 20) ÷ 5 = -4 m/s²

17. A train moving at 40 m/s slows down at a rate of -2 m/s². How long does it take to stop?
    
    

    • t = 40 ÷ 2 = 20 seconds

18. A rock is dropped from a cliff and falls freely under gravity. How fast is it moving after 3 seconds?
    
    

    • v = g × t = 9.8 × 3 = 29.4 m/s

19. A car accelerates from rest at 4 m/s² for 6 seconds. What is its final velocity?
    
    

    • v = 0 + (4 × 6) = 24 m/s

20. A runner completes a 400-meter lap in 50 seconds. What is their average speed?
    
    

    • v = 400 ÷ 50 = 8 m/s

Bonus Question

A rocket accelerates from 0 to 500 m/s in 25 seconds. What is its acceleration?

• a = (500 - 0) ÷ 25 = 20 m/s²

Study Tip:

• Memorize the key formulas:

  • Speed: v = d ÷ t

  • Acceleration: a = Δv ÷ Δt

  • Final velocity: v = u + at

• Understand how graphs represent motion.

• Practice solving different types of motion problems!