3.1 Motion

Question 1

Define speed, the equation used to calculate speed, and the respective SI units:

Answer 1

Speed is defined as the rate of change of distance. The equation used is

speed = distance / time

The SI units are ms^-1

Question 2

Define displacement:

Answer 2

The displacement of an object is the distance it has travelled in a given direction, so it is a vector with both magnitude and direction

Question 3

Define velocity, the equation used to calculate velocity, and the respective SI units:

Answer 3

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

The equation used is:

velocity = change in displacement/time

The SI units are ms^-1

Question 4

Define acceleration, the equation used to calculate acceleration, and the respective SI units:

Answer 4

Acceleration is defined as the rate of change of velocity, making it a vector

The equation used is:

acceleration = change in velocity/time

The SI units are ms^-2

Question 5

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

Answer 5

A stationary object

Question 6

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

Answer 6

An object moving with constant velocity

Question 7

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

Answer 7

Acceleration (if gradient is increasing)

Deceleration (if gradient is decreasing)

Question 8

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

Answer 8

An object moving with constant velocity

Question 9

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

Answer 9

An object is accelerating (positive gradient)

An object is decelerating (negative gradient

Question 10

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

Answer 10

Displacement

Question 11

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

Answer 11

Velocity

Question 12

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

Answer 12

• 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 using an equation of motion

Question 13

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

Answer 13

• 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 light gates when they pass
• Keep one cart stationary and push the other towards it, measuring it’s velocity before the collision
• Then measure the velocity of both carts after the collision and calculate the momentum before and after

Question 14

Define “g”

Answer 14

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 = 9.81 ms^-2

Question 15

Describe the experiment in which one can determine “g” using an electromagnet

Answer 15

• 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 at^2
• Calculate ‘a’ which, in this case, is ‘g’

Question 16

A ball is projected off a castle at 6ms^-1. How does its horizontal velocity change from its launch until it hits the ground?

Answer 16

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

Question 17

In projectile motion, what is the vertical acceleration?

Answer 17

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