Topic 5c- Forces and motion

Question 1

What is displacement?

Answer 1

A vector quantity measuring the distance and direction that an object has moved from its starting to finishing point.

Question 2

What is the difference between speed and velocity?

Answer 2

• Both measure how fast you’re going
• velocity has a direction (e.g. 20m/s on a bearing of 060°)

Question 3

What’s an example where an object has a consistent speed but a constantly changing velocity?

Answer 3

An object going round in a circle

Question 4

What is the typical speed of a person walking?

Answer 4

1.5m/s

Question 4

What is the typical speed of a person running?

Answer 4

3m/s

Question 5

What is the typical speed of a person cycling?

Answer 5

6m/s

Question 6

What is the typical speed of a car?

Answer 6

25m/s

Question 7

What is the typical speed of a train?

Answer 7

55m/s

Question 8

What is the typical speed of a plane?

Answer 8

250m/s

Question 9

What is the speed of sound in air?

Answer 9

330m/s

Question 10

What is acceleration?

Answer 10

• Acceleration is how quickly the velocity is changing
• this change in velocity can be a change in speed, or a change in direction, or both

Question 11

Ways to increase top speed of a vehicle

Answer 11

1. reduce drag → make more streamilined
2. increasing power of vehicle’s engine

Question 12

What are the three stages of falling in a fluid?

Answer 12

1. at the start, the object accelerates downwards due to the force of gravity
2. as the object’s speed increases, frictional forces such as air resistance or drag increase
3. at terminal velocity, the weight of the object due to gravity is balanced by the frictional forces, and the resultant force is zero

Question 13

Explain what happens to a skydiver when they jump, reach terminal velocity, and then open their parachute

Answer 13

1. On leaving the aircraft, the skydiver accelerates downwards due to the force of gravity.
2. There is no air resistance acting in the upwards direction, and there is a resultant force acting downwards so the skydiver accelerates towards the ground.
3. As the skydiver gains speed, the air resistance increases. There is still a resultant force acting downwards, but this gradually decreases.
4. Eventually, the skydiver’s weight is balanced by the air resistance. There is no resultant force and the skydiver reaches terminal velocity.
5. When the parachute opens, the air resistance increases as there is a greater area for air particles to collide with.
6. The skydiver slows down until a new, lower terminal velocity is reached.

Question 14

What is inertia?

Answer 14

How difficult it is to change the velocity of an object depending on it’s mass (e.g. its harder to stop a bowling ball than a golf ball)