Module 3 - Forces and Motion

Question 1

Acceleration

Answer 1

The rate of change of velocity

Question 2

Average speed

Answer 2

Distance over time for the entire region of interest

Question 3

Braking distance

Answer 3

The distance travelled between the breaks being applied and the vehicle coming to a stop. It is affected by the vehicle and road conditions.

Question 4

Displacement

Answer 4

The direct distance between an object’s starting and ending positions
It is a vector quantity and so has both a direction and magnitude

Question 5

Displacement - Time graphs

Answer 5

Plots showing how displacement changes over a period of time
The gradient gives the velocity
Curved lines represent an acceleration

Question 6

Free-Fall

Answer 6

An object is said to be in free fall when the only force acting on it is the force of gravity

Question 7

Instantaneous speed

Answer 7

The exact speed of an object at a specific given point

Question 8

Projectile motion

Answer 8

The motion of an object that is fired from a point and then upon which only gravity acts.
(when solving projectile motion problems, it is useful to split the motion Into horizontal and vertical components)

Question 9

Reaction time

Answer 9

The time taken to process a stimulus and trigger a response to it. It is affected by alcohol, drugs and tiredness.

Question 10

Stopping distance

Answer 10

The sum of thinking distance and breaking distance for a driven vehicle

Question 11

Thinking distance

Answer 11

The distance travelled in the time it takes for the driver to react. It is affected by alcohol, drugs and tiredness.

Question 12

Velocity - Time graphs

Answer 12

Plots showing how velocity changes over a period of time.
The gradient gives acceleration.
Curved lines represent changing acceleration.

Question 13

Velocity

Answer 13

The rate of change of displacement.
It is a vector quantity and so has both a direction and magnitude.

Question 14

What does a straight, horizontal line represent on a displacement-time graph?

Answer 14

A stationary object

Question 15

What does a line with a constant, non-zero gradient represent on a displacement-time graph?

Answer 15

An object moving with constant velocity.

Question 16

What does a curved line represent on a displacement-time graph?

Answer 16

Acceleration (if gradient is increasing)
Deceleration (if gradient is decreasing)

Question 17

What does a straight, horizontal line represent on a velocity-time graph?

Answer 17

An object moving with constant velocity.

Question 18

What does a line with a constant, non-zero gradient represent on a velocity-time graph?

Answer 18

An object that is accelerating (positive gradient)
An object that is decelerating (negative gradient)

Question 19

What does the area under a velocity-time graph represent?

Answer 19

Displacement

Question 20

What does the area under an acceleration-time graph represent?

Answer 20

Velocity

Question 21

Describe how the terminal velocity of an object can be determined using light gates.

Answer 21

Set up the light gates vertically and measure the distance between them.
Connect them to a data logger and then release an object from rest above them, measuring the time it takes for the object to travel between the two gates.
Using the time and the known distance, you can calculate the velocity of the falling object.

Question 22

Describe how light gates can also be used to investigate conservation of momentum.

Answer 22

Place two carts on a linear air track (to reduce friction) with repelling magnets so that they do not stick together.
Attach card to the top of each cart so that they break the beams of the light gates when they pass.
Keep one cart stationary and push the other towards it, measuring its velocity before the collision.
Then measure the velocity of both carts after the collision and calculate the momentum before and after.

Question 23

Define ‘g’.

Answer 23

It is the acceleration of an object in response to the gravitational attraction between the earth and the object.

Question 24

Describe the experiment in which one can determine ‘g’ using an electromagnet.

Answer 24

An electromagnet holds a steel ball suspended a measured distance above a surface, then start the timer when the electromagnet is deactivated, and stop it when the surface is hit.
As the ball was initially resting, u = 0
The distance and time are known, so we can use the SUVAT equation: s = ut + 1/2at^2t
Calculate ‘a’ which, in this, is ‘g’.

Question 25

A ball is projected off a castle at 6m/s. How does its horizontal velocity change from its launch until it hits the ground?

Answer 25

The horizontal velocity remains the same as there is no acceleration in the horizontal direction.

Question 26

In projectile motion, what is the vertical acceleration?

Answer 26

The vertical acceleration is equal to the gravitational field strength (g) downwards.