P2.1 Motion

Question 1

How can you measure very short periods of time accurately?

Answer 1

• You can use light gates
• A timer starts and stops when an object interrupts a light beam

Question 2

What is ultrasound and what are its uses?

Answer 2

• Ultrasound is high-frequency sound waves used to measure distance
• This device measures the time taken for a pulse to travel there and back
• It uses this value, the speed of the pulse, to work out the distance

Question 3

What is uniform motion?

Answer 3

Motion in which speed does not change

Question 4

What is non-uniform motion?

Answer 4

Motion where the speed changes

Question 5

What is the SI unit for distance?

Answer 5

Metres

Question 6

What is the SI unit for time?

Answer 6

Seconds

Question 7

What is a vector?

Answer 7

• A vector is a quantity that has a magnitude and a direction
• Force is a vector
• You represent a vector with an arrow
• The length of the arrow shows the magnitude, and the direction of the arrow shows the direction

Question 8

What is a scalar?

Answer 8

• The measurement that you make with a stop clock is a scalar
• It has a magnitude, but no direction

Question 9

What is the difference between displacement and distance?

Answer 9

• Distance is a scalar
• Displacement is a vector, so it has direction as well

Question 10

What is the difference between speed and velocity?

Answer 10

• Speed is a scalar quantity, so 15 m/s is a measurement of speed
• Velocity is a vector quantity, it has a direction as well as magnitude, so 15 m/s south is a velocity

Question 11

How do you add vector quantities?

Answer 11

You can add vectors, but you must take into account the + sign or the - sign

Question 12

What is acceleration?

Answer 12

The change in velocity per second

Question 13

What does uniform acceleration mean?

Answer 13

It means that the acceleration does not change

Question 14

Is it better to say ‘negative acceleration’ or ‘deceleration’?

Answer 14

It is better to say ‘negative acceleration’ rather than ‘deceleration’

Question 15

What is the acceleration due to gravity?

Answer 15

• 9.81 m/s², or about 10 m/s²
• Another way of thinking about this acceleration is that when something is falling vertically, during each second its downward velocity increases by about 10 m/s

Question 16

What does a graph of distance against time mean?

Answer 16

• A graph of distance against time tells you about the speed of an object on its journey
• The speed is equal to the gradient (or slope) of the graph
• A straight line means the object’s speed is constant because the gradient does not change
• A horizontal line means that the object is not moving
• The steeper the line, the faster the object is travelling

Question 17

How is a distance-time graph different from a displacement-time graph?

Answer 17

• A distance-time graph shows the total distance travelled
• If you plot a displacement-time graph, then the gradient can be positive, zero, or negative
• The gradient of the graph is the velocity, so it has a direction as well as a magnitude

Question 18

What can you deduce from the gradient of a graph?

Answer 18

• The gradient of any graph with time on the x-axis tells you about a rate of change with time
• The rate of change of speed or velocity with time tells you the acceleration

Question 19

How do you calculate distance travelled?

Answer 19

• The distance travelled is the area under a speed-time graph
• The displacement is the area under a velocity-time graph
• You can find the area by using triangles, rectangles, or by counting squares
• You multiply speed and time to get distance

Question 20

What is a kinetic store?

Answer 20

• Energy can be transferred to and from a kinetic store
• A store is a system for which we can do an energy calculation - energy is a quantity (a number with joules as the unit)

Question 21

Kinetic energy (energy in a kinetic store) equation:

Answer 21

Kinetic energy (J) = 0.5 x mass (kg) x (speed(m/s))2