Motion

Question 1

Scalar quantity

Answer 1

A quantity with magnitude but no direction

Question 2

Vector quantity

Answer 2

A quantity with magnitude and direction

Question 3

Speed

Answer 3

Rate of change of distance travelled

Question 4

Average speed

Answer 4

Total distance travelled divided by the time taken

Question 5

How could you use standard laboratory equipment to determine the average speed at which a marble rolls down a slope? Include quantities which you measure and equipment used.

Answer 5

1) measure the distance the marble travels between two marked points using a meter ruler / tape measure

2) measure the time take for the marble to travel between two marked points using a stopwatch

3) using speed= distance/time calculate the average speed of the marble

Question 6

Suggest why your value may differ from that of a value obtained using a radar speed trap.

Answer 6

-Zero error: not starting watch at 0
-delay in reaction time for starting and stopping watch
-measurement error (parallax) on time measurement

Question 7

Hoe can you use light gates to measure average speed over a fixed distance?

Answer 7

1) connect two light gates to an electronic timer. When the object passes through the first light gate, the timer will start. When the object passes through the second gate the timer will stop.

2) measure the distance that the object has travelled between the two light gates using a meter ruler.

3) using speed = distance/time, calculate the average speed of the object

Question 8

Displacement

Answer 8

Distance moved in a stated direction (in a straight line)

Question 9

Velocity

Answer 9

Rate of change of displacement

Question 10

Acceleration

Answer 10

Rate of change of velocity

Question 11

Explain how Galileo disproved the idea that “heavier objects fall faster than lighter ones”.

Answer 11

two cannonballs of different mass (but same size) are dropped from the same height at the same time.

They hit the ground at the same time so both have the same acceleration

Question 12

Describe an experiment to estimate the acceleration g of free fall. Include:
-measurements taken/equipment used
-how the measurements are used to estimate g
-an explanation of why the value g is an estimate

Answer 12

1) measurements taken/equipment used:
-measure the distance the ball falls using a meter ruler (or tape measure)
-measure the time the ball is falling for using a stopwatch

2)how the measurements are used to estimate g
-s= ut+ 1/2at^2 and u=0m/s and so s=1/2at^2
-Plot a graph of s vs t^2, and g=2* gradient

3) an explanation why the value of g is an estimate:
- drag (air resistance) acting on the ball is ignored
-There is a reaction time on starting and stopping the stopwatch
-Parallax errors with the time at which the ball hits the ground are not accounted for

Question 13

What is the thinking distance?

Answer 13

Distance travelled from when the driver sees a problem and the brakes are applied.

Question 14

What is the braking distance?

Answer 14

Distance travelled from when the driver starts braking to when the car stops

Question 15

What is the stopping distance?

Answer 15

Distance travelled from when the driver sees a problem to when the car stops
(Thinking distance + braking distance)

Question 16

Describe and explain factors that increase the braking distance of a car.

Answer 16

1) A greater speed: braking distance is directly proportional to the speed squared.
2) A greater mass: braking distance is directly proportional to the mass
3) Worn tyres/brakes: friction acting between the car and the road increases
4) wet / slippery/ icy roads roads: friction acting between the car and road decreases
5) A downhill slope: the component of acceleration parallel to the slope increases

Question 17

Describe the factors that increases the thinking distance of a car.

Answer 17

1) consumption of drugs/alcohol
2) driver fatigue / distractions
3) A greater speed: a greater distance is travelled during the reaction time

Question 18

How does braking distance depend on the speed and mass of the vehicle?

Answer 18

-Braking distance is directly proportional to speed^2
-braking distance is directly proportional to the mass

Question 19

Define acceleration

Answer 19

Rate of change of velocity

Question 20

When solving projectile motion problems on Earth, what assumption is made regarding acceleration?

Answer 20

1) air resistance is not taken into account.
2) vertical component of acceleration = -9.81ms^-2.
3) horizontal component of acceleration = 0ms^-2

Question 21

Define instantaneous speed.

Answer 21

The speed at a particular time

Question 22

How does thinking distance depend on the speed of the vehicle?

Answer 22

Thinking distance is directly proportional to the speed

Question 23

For a projectile, how do you calculate the time of flight of the object?

Answer 23

1) calculate the time taken for the object to reach maximum height (vertical component of velocity=0)
2) multiply the answer by 2.

Question 24

For a projectile, how do you calculate the time of flight of the object?

Answer 24

1) calculate the time taken for the object to reach maximum height (vertical component of velocity = 0)
2) multiply the answer by 2.

Question 25

What does the gradient of a velocity-time graph represent?

Answer 25

Acceleration

Question 26

How do you calculate the stopping distance?

Answer 26

Stopping distance = thinking distance + braking distance