Acceleration

Question 1

True or false? A negative change in speed shows an object has decelerated

Answer 1

True

A negative change in speed gives a negative acceleration, which is deceleration

Question 2

What’s the equation that links acceleration, time taken and change in velocity?

Answer 2

acceleration = change in velocity / time taken or a = (v-u) / t

Question 3

What is the magnitude of acceleration due to gravity on Earth?

Answer 3

10 m/s^2

For objects in free fall near the Earth’s surface the magnitude of acceleration due to gravity is equal to 10 m/s^2

Question 4

Tanvi is cycling down a street when a pedestrian crosses the road in front of her. She brakes and decelerates at 3 m/s2 for 2.5 seconds.
What is her change in velocity?

Answer 4

7.5 m/s

a = (v-u) / t, so the change in velocity = a x t = 3 x 2.5 = 7.5 m/s

Question 5

A thief walks past a man and snatches his phone. She starts to run in the same direction as she was walking in. It takes her 2 seconds to reach her running speed. Estimate her acceleration

Answer 5

0.8 m/s^2
Given the thief’s walking speed = 1.4 m/s and her running speed = 3 m/s, her change is velocity (v-u) is approximately 3 - 1.4 = 1.6 m/s.
a = (v-u) / t, so her acceleration = 1.6 / 2 = 0.8 m/s^2

Question 6

A stationary vulture hovering 3.2 m above the ground drops Sandra. Calculate the final velocity of Sandra as she hits the ground. Use the formula: (final velocity)^2 - (initial velocity)^2 = 2 x acceleration x distance

Answer 6

8 m/s
v^2 - u^2 = 2 * a * x, rearranging for v^2 gives v^2 = 2 * a * x + u^2
a = 10 m/s^2, so v^2 = (2 x 10 x 3.2) + 0^2 = 64
So v = √64 = 8 m/s