5.6 Forces and motion

Question 1

What is distance? (1)

Answer 1

How far an object moves

Question 2

What is displacement? (1)

Answer 2

The direct (straight) distance from the start to finish point with its direction.

Question 3

What can be said about the speed of a moving object, sound and wind? (1)

Answer 3

It is rarely constant.

Question 4

What factors affect the speed at which a person can walk, run or cycle? (3)

Answer 4

• Age
• Terrain
• Distance travelled

Question 5

What is the typical speed of walking, running and cycling? (3)

Answer 5

Walking: 1.5 m/s
Running: 3 m/s
Cycling: 6 m/s

Question 6

What is the typical speed of sound in air? (1)

Answer 6

330 m/s

Question 7

What is the equation for an object moving at constant speed? (1)

Answer 7

Distance (m) = speed (m/s) x time (s)

Question 8

What is velocity? (1)

Answer 8

An object’s speed in a given direction.

Question 9

Why can an object moving at a constant speed not have a constant velocity in a circle? (3)

Answer 9

1. Velocity is a vector quantity
2. When moving in a circle there is a continuos change in direction
3. The only way velocity can be constant is if the direction is also the same.

Question 10

What are distance-time graphs used to represent? (1)

Answer 10

The distance travelled in a straight line.

Question 11

How can the speed be calculated in a distance-time graph? (1)

Answer 11

Gradient.

Question 12

How do you calculate the speed for an accelerating object? (2)

Answer 12

1. Draw a tangent to the curve at the required time.
2. Calculate the gradient of tangent.

Question 13

What is the equation for the average acceleration of an object? (1)

Answer 13

Acceleration (m/s²) = change in velocity (m/s) / time taken (s)

Question 14

How can the acceleration be calculated in a velocity-time graph? (1)

Answer 14

Gradient.

Question 15

How can the distance travelled by an object be calculated in a velocity-time graph? (1)

Answer 15

The area under the graph.

Question 16

What is the equation for uniform acceleration? (1)

Answer 16

(final velocity)² - (initial velocity) ² = 2 x acceleration (m/s ²) x distance (m)

Question 17

What is the acceleration of any object free falling under gravity near Earth’s surface? (1)

Answer 17

9.8 m/s²

Question 18

What happens for an object to reach terminal velocity in a fluid? (2)

Answer 18

1. Initially the object accelerates due to gravity
2. Eventually, the resultant force will be zero so the object reaches its terminal velocity (meaning the object will move at a constant speed).

Question 19

What is Newton’s first law? (2)

Answer 19

Stationary: if resultant force is 0, then object will remain at rest.
Moving: if resultant force is 0, then object will stay at constant velocity (same speed and direction).

Question 20

What happens to the forces when a vehicle travels at a constant speed? (1)

Answer 20

The resistive force balances out the driving force.

Question 21

What force is only able to change the velocity (speed and/or distance) of an object? (1)

Answer 21

Resultant force

Question 22

What is inertia? (1)

Answer 22

The tendency of an object to remain in its state of rest or uniform motion.

Question 23

What is Newton’s second law? (1)

Answer 23

The acceleration of an object is directly proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.

F = ma

Question 24

What is the equation for Newton’s second law? (1)

Answer 24

Force (N) = mass (kg) x acceleration (m/s ²)

Question 25

What is the equation for Newton’s second law? (1)

Answer 25

Resultant force (N) = mass (kg) x acceleration (m/s ²)

Question 26

What is inertial mass? (1)

Answer 26

A measure of how difficult it is to change the velocity of an object, expressed as the ratio of force over acceleration.

Question 27

What is Newton’s third law? (1)

Answer 27

Whenever two objects interact, the forces they exert at each other are equal and opposite.

Question 28

What is the stopping distance of a vehicle? (1)

Answer 28

The sum of the vehicle’s distance travelled during the driver’s reaction time/thinking distance and the distance travelled under the braking force/distance.

Question 29

What is the conclusion for a given braking force? (1)

Answer 29

The greater the speed, the greater the breaking force required to stop the vehicle in a certain distance.

Question 30

What is the range of typical human reaction times? (1)

Answer 30

0.2 s to 0.9 s

Question 31

What are factors that can affect a driver’s reaction time? (3)

Answer 31

- Drugs - Alcohol - Tiredness

Question 32

What is a simple method that can be used to measure human reaction time? (2)

Answer 32

1. Person has to respond to visual or auditory stimulus as quickly as possible. 2. Time taken to respond is recorded and used as measure of their reaction time.

Question 33

What factors can affect braking distance? (2)

Answer 33

- Adverse road and weather conditions - icy/wet conditions - Poor vehicle condition - tyre/brake conditions

Question 34

Explain what happens when someone presses the brakes. (1)

Answer 34

- Force applied to brakes - causes work done by friction force - between brakes and wheel - to reduce kinetic energy of vehicle - and increase temperature of wheel.

Question 35

What is the conclusion about decelration and braking force? (1)

Answer 35

The greater the braking force, the greater the vehicle’s deceleration.

Question 36

What are the dangers of large decelerations? (2)

Answer 36

- Brakes overheating - Loss of control of vehicle