Simplified P3 - Speed, Changing Speed, Forces & Motion

Question 1

Why do we write average speed?

Answer 1

We write average speed because the speed of a car can change throughout the journey.

Question 2

What is instantaneous speed?

Answer 2

It is the speed of a car at a certain point.

Question 3

What happens if you increase the speed?

Answer 3

If you increase the speed, it means increasing the distance travelled in the same time,
increasing the speed reduces the time needed to over the distance.

Question 4

What does the gradient of a distance-time graph tell you?

Answer 4

The gradient of a distance-time graph tells you about the speed of the object.

Question 5

What happens to the gradient if you increase the speed?

Answer 5

A higher speed means a steeper gradient, therefore as you increase the speed, the gradient will become steeper.

Question 6

What does a straight line on a distance time graph indicate?

Answer 6

A straight line indicates that the speed is constant.

Question 7

What does a curved line show on a distance time graph?

Answer 7

It shows that the speed is changing, the speed is not constant.

Question 8

What is acceleration?

Answer 8

A change of speed per unit time is called acceleration.

Question 9

When would an object be accelerating?

Answer 9

If the speed is increasing, the object is accelerating.

Question 10

When would an object be decelerating?

Answer 10

When the speed is decreasing, the object is decelerating.

Question 11

What does the area under the speed time graph tell you?

Answer 11

The area under a speed time graph is equal to the distance travelled.

Question 12

What is acceleration measured in?

Answer 12

Acceleration is measured in metres per second squared (m/s2).

Question 13

What does a negative acceleration show about the car?

Answer 13

It shows that the car is decelerating.

Question 14

Is velocity vector or scalar, and why?

Answer 14

Velocity is a vector, this is because it has both size ( speed ) and direction.

Question 15

What is relative velocity ( if the cars are going in opposite directions )?

Answer 15

The sum of their individual velocities if they are going in opposite directions.

Question 16

What is relative velocity ( if the cars are going in the same direction)?

Answer 16

The difference of their individual velocities if they are going in the same direction.
e.

Question 17

Why is a vehicle travelling around a roundabout accelerating and not travelling at a constant speed?

Answer 17

• A vehicle around a roundabout may be moving at a constant speed, but it is infact accelerating.
• The direction of travel is constantly changing, it is not going in a straight line, the driver needs to apply a force towards the centre of the roundabout to change direction, this gives the vehicle an acceleration directed towards the centre of the roundabout.

Question 18

Where does any object moving around a circle travel, relative to the circle?

Answer 18

Any object moving along a circular path moves at a tangent to the circle, or arc of the circle.

Question 19

What happens if the forces acting on an object are balanced?

Answer 19

If the forces acting on an object are balanced then the object is at rest, or has a constant speed.

Question 20

What happens if the forces acting on an object are unbalanced?

Answer 20

• The object will either:
  Slow down
  Speed Up

Question 21

What is the unit of force?

Answer 21

The unit of force is the newton ( N ).

Question 22

What factors can increase reaction time?

Answer 22

Reaction time , and therefore thinking distance may increase if a driver is:

• Tired
• Under the influence of alcohol or other drugs.
• Travelling Faster
• Distracted or lacks concentration

Question 23

What factors may increase braking distance?

Answer 23

• Breaking distance may increase if:
• The road conditions are poor, e.g. Icy, wet.
• The car has not been properly maintained, e.g. worn out tire tread, worn out/ damaged brakes.
• The speed is increased.

Question 24

What factors AFFECT braking distance?

Answer 24

• The greater the mass of the vehicle, the greater its braking distance
• The greater the speed of a vehicle, the greater its braking distance.
• When the brakes are applied, the brake pads are pushed against the disc, this creates a large friction force that slows the car down, worn brakes reduce the friction force, increasing the braking distance.
• Worn tyres with very little tread reduce the grip of the wheels on a slippery road, leading to skidding and increase in braking distance
• Increased braking force reduces the stopping distances.

Question 25

How are thinking distance and speed correlated?

Answer 25

Thinking distance increases linearly with speed.

Question 26

What relationship does braking distance increase in?

Answer 26

Braking distance increases as a squared relationship.

e.g. the braking distance is 60mph is nine times the braking distance at 20mph.