3.1 Motion

Question 1

How is average speed calculated?

Answer 1

Average speed (ms-1) = Distance Travelled (m)/Time Taken (s)

Question 2

What is gradient equal to on a distance time graph?

Answer 2

The gradient is equal to speed.
If the gradient is 0, the object is stationary.

Question 3

What is instantaneous speed?

Answer 3

Instantaneous speed is the speed of something over a short interval of time.

Question 4

What is the difference between distance and displacement?

Answer 4

Displacement shows how far something is from the starting point, distance shows the overall total of how far something has travelled.

Question 5

What is the difference between speed and velocity?

Answer 5

Speed is scalar and only has magnitude, velocity is vector and has both magnitude and direction.

Question 6

How is average velocity calculated?

Answer 6

Average Velocity (ms-1) = Change in Displacement (m)/Time Taken (s)

Question 7

How is velocity determined from a displacement time graph?

Answer 7

Velocity is calculated from the gradient, or on a curve, by drawing a tangent.

Question 8

How is acceleration defined?

Answer 8

Acceleration is the rate of change in velocity.
Acceleration (ms-2) = Change in Velocity(ms-1)/Time Taken (s)

Question 9

How is acceleration determined from a velocity time graph?

Answer 9

Acceleration is calculated from the gradient of the graph.

Question 10

How is displacement determined from a velocity time graph?

Answer 10

Displacement is calculated from the area of the graph.

Question 11

What type of motion is SUVAT used for?

Answer 11

Motion in a straight line with constant acceleration.

Question 12

What are the SUVAT equations?

Answer 12

v=u+at
s=ut+1/2at²
s=vt-1/2at²
s=1/2(u+v)t
v²=u²+2as

Question 13

What is meant by free fall?

Answer 13

When an object is accelerating under gravity, it is said to be in free fall.

Question 14

What is the value of acceleration due to gravity?

Answer 14

9.81ms-2

Question 15

What is the electromagnet/trapdoor method of determining g?

Answer 15

• An electromagnet holds a small steel ball above a trapdoor.
• When the current is switched off, a timer is triggered and the electromagnet will demagnetise and the ball falls.
• When it hits the trapdoor, electrical contact is broken and the timer stops.
• The value for g is calculated from the height of the fall - measured with a metre rule - and the time taken.

Question 16

What is the light gate method of determining g?

Answer 16

• Light gates with two light beams, detectors and a timer connected on a software can be used.
• When the ball is dropped and falls through the first beam, light is interrupted and the timer starts.
• When it falls to the second beam, the timer stops.
• The value for g is calculated from the height between the light gates - measured with a metre rule - and the time taken.

Question 17

What is the picture taking method of determining g?

Answer 17

• A small metal ball is dropped from rest next to a metre rule, and its fall is recorded on video, or pictures are taken with a rapid-fire repeating mode.
• Instead, a stroboscope illuminates with rapid flashes and the camera shutter is held open which produces many photos of the fall.
• The position of the ball at regular intervals is recorded against the metre rule. Time taken is measured with a stopwatch in frame of the camera.

Question 18

Describe how data from the determining g experiments can determine g.

Answer 18

Plot a graph of s against t². The value of g is determined from s=ut+1/2at² but s=1/2gt² can be used as it’s dropped from rest.

Question 19

How is stopping distance defined?

Answer 19

Stopping Distance = Thinking Distance + Braking Distance

Question 20

How is thinking distance defined?

Answer 20

Thinking distance is the distance moved between the driver seeing an obstruction and applying the brakes, it depends on the driver’s reactions.

Question 21

What is the equation for thinking distance?

Answer 21

Thinking Distance = Reaction Time x Speed of the Car

Question 22

What causes thinking distance to vary?

Answer 22

If the driver is tired, under the influence, or speed is increased, thinking distance increases.

Question 23

How is braking distance defined?

Answer 23

Braking distance is the distance moved after applying the brakes until the vehicle stops.

Question 24

What causes braking distance to vary?

Answer 24

It will increase if the mass is large, velocity is higher, it is raining/icy/muddy, or car brakes/tyres are worn, which both result in less friction.