Motion and Safety

Question 1

When can an object travelling at a
constant speed not have a constant
velocity? (Higher)

Answer 1

When the object is changing direction;

for example, moving in a circle.

Question 2

Why does an object travelling at a constant speed in

a circle not have a constant velocity? (Higher)

Answer 2

● Speed is a scalar quantity
● Velocity is a vector quantity which means it can
only be constant if the direction is constant
● In circular motion, the direction is continuously
changing
● Velocity is constantly changing

Question 3

What is the resultant force that acts on an object
moving in a circle called, and in which direction does
it act? (Higher)

Answer 3

It is called the centripetal force and acts

towards the centre of the circle.

Question 4

What is inertial mass? (Higher)

Answer 4

● A measure of how difficult it is to
change a given object’s velocity
● The ratio of force over acceleration

Question 5

State Newton’s Third Law. (Higher)

Answer 5

Whenever two objects interact, the
forces that they exert on each other are
always equal and opposite.

Question 6

State the equation used to calculate an object’s

momentum. (Higher)

Answer 6

Momentum = Mass x Velocity

Question 7

What is the unit used for momentum? (Higher)

Answer 7

kgm/s

kilogram metres per seconds

Question 8

In a closed system, what can be said about the

momentum before and after a collision? (Higher)

Answer 8

The total momentum before and after are

equal.

Question 9

State an equation linking change in momentum,

force and time. (Higher)

Answer 9

Force x Time = Change in Momentum

Question 10

How can you measure human reaction

times?

Answer 10

● Using the ruler drop test
● PersonAand B hold each end of a ruler with the 0 cm
mark at the bottom
● PersonAdrops the ruler without telling person B
● Person B catches it
● The distance travelled corresponds to their reaction
time

Question 11

Why is it important that the 0cm mark is at the

bottom?

Answer 11

So you can obtain the distance directly
without having to calculate it; otherwise,
a zero error would need to be accounted
for.

Question 12

What is the stopping distance of a vehicle equal to?

Answer 12

The sum of thinking distance and braking

distance.

Question 13

For a given braking distance, if the vehicle’s speed is
increased, what can be said about its stopping
distance?

Answer 13

The stopping distance is increased with

an increase in speed.

Question 14

Give a typical range of values for human reaction

time.

Answer 14

0.2 seconds - 0.9 seconds

Question 15

Give three factors which can affect a driver’s

reaction time.

Answer 15

1. Tiredness
2. Drugs
3. Alcohol

Question 16

Give two factors which may affect braking distance.

Answer 16

1. Adverse (wet/icy) road conditions

2. Poor tyre/brake conditions

Question 17

Describe the energy transfers that take place when a

car applies its brakes.

Answer 17

● Work is done by the friction force between
the brakes and wheel
● Kinetic energy of the wheel is converted to
heat and is dissipated to the surroundings
through the brake discs

Question 18

To stop a car in a given distance, if its velocity is
increased, what must happen to the braking force
applied?

Answer 18

The braking force must also be

increased

Question 19

State two consequences of a vehicle undergoing

very large decelerations.

Answer 19

1.Kinetic energy converted to heat is
very high causing brakes to overheat
2. Loss of control of the vehicle