Science HW

Term

Definition

Acceleration

Acceleration is the rate of change of velocity.

22. An airplane starts at rest and accelerates down the runaway for 20 s. At the end of the runaway, its velocity is 80 m/s north. What is its acceleration?

1. V_f  = V_i + at

2. 80 m/s = 0 + a ⋅ 20 s

3. 80 m/s = 0 + 20 s ⋅ a

4. 80 m/s = 20 s ⋅ a

5. 80 m/s ÷ 20 s = 20 s ⋅ a ÷ 20 s

6. A = 4 m/s²

The airplane's acceleration was 4 m/s².

24. A ball is dropped and falls with an acceleration of 9.8 m/s² downward. It hits the ground with a velocity of 49 m/s downward. How long did it take the ball to fall to the ground?

1. T = V - V² ÷ a

2. T = 49 - 0 ÷ 9.8

3. T = 49 ÷ 9.8

4. T = 5

It took 5 seconds for the ball to drop.

23. A cyclist starts at rest and accelerates at 0.5 m/s² south for 20 s. What is the cyclist’s final velocity?

1. V_f  = V_i + at

2. V_f  = 0 + 0.5 m/s²  ⋅ 20 s

3. V_f  = 0 + 10 m/s

4. V_f  = 10 m/s

The cyclist’s final velocity was 10 m/s

26. Determine the change in velocity of a car that starts at rest and has a final velocity of 20 m/s north.

1. ∆_v  = V_f - V_i

2. ∆_v = 20 m/s - 0 m/s

3. ∆_v = 20 m/s

The change in velocity of the car is 20 m/s north.

27. Describe the motion of an object that has an acceleration of 0m/s²

1. A  = 0 m ÷ s²

• Acceleration is the rate of change of velocity.

• Velocity is the rate of change in position.

• If acceleration is zero, the velocity is constant.

• Constant velocity means the object is either at rest or moving in a specific direction with a constant speed.

The object is either at rest or moving at a constant velocity.

29. Calculate the time; A ball is dropped from a cliff and has an acceleration of 9.8 m/s². How long will it take the ball to reach a speed of 24.5 m/s?

1. V_f  = V_i + at

2. 24.5 m/s = 0 + 9.8 m/s² ⋅ t

3. 24.5 m/s = 9.8 m/s² ⋅ t

4. 24.5 m/s ÷ 9.8 m/s² = 9.8 m/s² ÷ 9.8 m/s²

5. T = 2.5 s

It takes the ball 2.5 seconds to reach a speed of 24.5 m/s.

30. Calculate the speed; A sprinter leaves the starting blocks with an acceleration of 4.5m/s². What is the sprinter's speed 2 s later?

1. V_f  = V_i + at

2. V_f  = 0 + 4.5 m/s² ⋅ 2 s

3. V_f  = 0 + 9 m/s

4. V_f  = 9 m/s

The sprinter’s speed 2 seconds later is 9 m/s.

An object can accelerate by change of speed, change of direction, or both change of speed and direction.

A person walking at 0 m/s and after 6 seconds is traveling at 5 m/s. What is the acceleration of the walker?

1. A = 5 m/s - 0 m/s ÷ 6 s

2. A = 5 m/s ÷ 6 s

3. A = 5/6 m/s²

4. A ≈ 0.83 m/s²

The acceleration of the walker is 0.83 m/s².

A car speeds up from 22 m/s to 26 m/s in 2 seconds. What is the average acceleration of the car? 

1. V_f  = V_i + at

2. 26 m/s = 22 m/s + a ⋅ 2 s

3. 26 m/s = 22 m/s + 2 s ⋅ a

4. 26 m/s = 2 s ⋅ a + 22 m/s

5. 26 m/s - 22 m/s = 2 s ⋅ a + 22 m/s - 22 m/s

6. 4 m/s = 2 s ⋅ a

7. 4 m/s ÷ 2 s = 2 s ⋅ a ÷ 2 s

8. A = 2 m/s²

The car’s average acceleration is 2 m/s².

Calculate the acceleration of the car. V_i = 0 m/s; t = 1.5 s; V_f  = 10.5 m/s

1. ∆_v  = V_f - V_i

2. ∆_v  = 10.5 m/s - 0 m/s

3. ∆_v  = 10.5 m/s

4. A = ∆_v ÷ t

5. A = 10.5 m/s ÷ 1.5 s

6. A = 7 m/s²

The acceleration of the car is 7 m/s².

The final velocity would be 42 m/s.

An object accelerating backwards.

It means the object is slowing down.