3.1 Motion

Question 1

Speed

Answer 1

Speed is defined as the rate of change of distance

Question 2

Instantaneous speed

Answer 2

is the speed of an object over a very short time interval. It can be determined by analysing the gradient of a distance-time graph at a given time

Question 3

Displacement

Answer 3

The displacement of an object is the distance it has travelled in a given direction, so it is a vector quantity, with both magnitude and direction. The velocity of an object is defined as the rate of change of displacement

Question 4

Acceleration

Answer 4

Acceleration is defined as the rate of change of velocity. Acceleration is a vector quantity. An object is accelerating when its speed is increasing, and decelerating when its speed decreases, and it will also accelerate when its direction of travel changes, such as in circular motion

Question 5

Velocity time graph

Answer 5

The area under the graph is equal to the displacement. Acceleration is the gradient. inital velocity is velocity which it starts at. final velocity is the velocity which it ends at

Question 6

What is a projectile

Answer 6

A projectile is an object that is thrown at an angle to the horizontal. and therefore moves in both the horizontal and vertical planes. The horizontal and vertical components of the object’s motion are analysed independently.

Question 7

What is the stopping distance

Answer 7

stopping distance = total distance = thinking distance + braking distance

Question 8

What is the Thinking distance

Answer 8

Thinking distance is the distance travelled between the moment the hazard is spotted, and the
moment the driver applies the brake

Question 9

What is the braking distance

Answer 9

The braking distance is the distance travelled from the time the brake is applied to the time the vehicle comes to a complete stop. The braking distance of the car is proportionate to the square of the initial speed of the car. The thinking distance is affected by the initial speed of the car

Question 10

How is thinking distance calculated

Answer 10

The thinking distance can be calculated by multiplying the initial speed of the car by the reaction time of the driver

Question 11

How is braking distance calculated

Answer 11

The braking distance of the car is proportionate to the square of the initial speed of the car

Question 12

Factors affecting thinking distance

Answer 12

such as tiredness, being under the influence of alcohol or drugs, and other distractions

Question 13

Factors affecting braking distance

Answer 13

road conditions (ice roads, wet), car conditions (heavy load, bald tires and poor brakes)

Question 14

Define velocity

Answer 14

The velocity of an object is defined as the rate of change of displacement, or speed in a given direction, making velocity a vector.

Question 15

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

Answer 15

A stationary object.

Question 16

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

Answer 16

An object moving with constant velocity.

Question 17

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

Answer 17

Acceleration (if gradient is increasing) or deceleration (if gradient is decreasing).

Question 18

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

Answer 18

Velocity.

Question 19

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

Answer 19

● Set up the light gates vertically and measure the distanc 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 20

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

Answer 20

● 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 21

Define ‘g’.

Answer 21

The acceleration of free fall, ‘g’, is the acceleration of an object in response to the gravitational attraction between the Earth and the object. g = 9.81m s-2

Question 22

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

Answer 22

● 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 a SUVAT equation: s = ut + 1⁄2 at2
● Calculate ‘a’ which, in this case, is ‘g’.

Question 23

A ball if projected of a castle at 6m s-1. How does its horizontal velocity change from its launch until it hits the ground?

Answer 23

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

Question 24

In projectile motion, what is the vertical acceleration?

Answer 24

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