P5 - Forces and motion

Question 1

Does a distance quantity require a
specific direction? i.e. Is it a scalar or
vector quantity?

Answer 1

No specific direction is required so it is a

scalar quantity.

Question 2

If an object moves 3 metres to the left
and then 3 metres back to its initial
position, what is the object’s total
displacement?

Answer 2

● The object has zero displacement
● Displacement is a vector quantity so it also
involves direction
● The object starts and ends at the same point

Question 3

State a typical value for the speed of

sound.

Answer 3

330 m/s

Question 4

What is a typical value for human

walking speed?

Answer 4

1.5 m/s

Question 5

What is a typical value for human

running speed?

Answer 5

3 m/s

Question 6

What is a typical value for human cycling

speed?

Answer 6

6 m/s

Question 7

State the equation linking distance,

speed and time. Give appropriate units.

Answer 7

Distance = Speed x Time

Distance (m), Speed (m/s), Time (s)

Question 8

Why can an object travelling at a constant speed in a circle not have a constant velocity?
(Higher)

Answer 8

● 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

Question 9

How can speed be calculated from a

distance-time graph?

Answer 9

The speed is equal to the gradient of the

graph.

Question 10

What must be done to calculate speed at
a given time from a distance-time graph
for an accelerating object? (Higher)

Answer 10

● Drawing a tangent to the curve at the required time

● Calculating the gradient of the tangent

Question 11

State the equation for the average acceleration of an object. Give appropriate units.

Answer 11

change in velocity (m/s) / time (s) = acceleration (m/s2)

Question 12

How can the distance travelled by an
object be calculated from a velocity-time
graph? (Higher

Answer 12

It is equal to the area under the graph

Question 13

Give an approximate value for the
acceleration of an object in free fall
under gravity near the Earth’s surface.

Answer 13

9.8 m/s²

Question 14

What can be said about the resultant force acting on an object when it is falling
at terminal velocity?

Answer 14

● The resultant force is zero

● When at terminal velocity, the object is moving at a constant speed and so isn’t accelerating

Question 15

State Newton’s first law for a stationary

object.

Answer 15

If the resultant force on a stationary
object is zero, the object will remain at
rest.

Question 16

State Newton’s first law for a moving

object.

Answer 16

If the resultant force on a moving object
is zero, the object will remain at constant
velocity (same speed in same direction).

Question 17

What can be said about the braking
forces and driving forces when a car is
travelling at constant velocity?

Answer 17

The braking forces are equal to the

driving forces.

Question 18

If an object changes direction but
remains at a constant speed, is there a
resultant force?

Answer 18

Since there is a change in direction,
there is a change in velocity and so there
must be a resultant force.

Question 19

What is inertia? (Higher)

Answer 19

The tendency of an object to continue in

its state of rest or uniform motion.

Question 20

State the defining equation for Newton’s

Second Law.

Answer 20

Resultant force = Mass x Acceleration

F = ma

Question 21

State Newton’s Second Law in words.

Answer 21

An object’s acceleration is directly
proportional to the resultant force acting
on it and inversely proportional to its
mass.

Question 22

What is inertial mass? (Higher)

Answer 22

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

Question 23

What is the symbol used to represent an

approximate value?

Answer 23

What is the symbol used to represent an

approximate value?

Question 24

State Newton’s Third Law.

Answer 24

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

Question 25

What is the stopping distance of a

vehicle equal to?

Answer 25

The sum of thinking distance and braking

distance.

Question 26

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

Answer 26

The stopping distance is increased with

an increase in speed.

Question 27

Give a typical range of values for human

reaction time.

Answer 27

0.2 seconds - 0.9 seconds

Question 28

Give three factors which can affect a

driver’s reaction time.

Answer 28

1. Tiredness
2. Drugs
3. Alcohol

Question 29

Give two factors which may affect

braking distance.

Answer 29

1. Adverse (wet/icy) road conditions

2. Poor tyre/brake conditions

Question 30

Describe the energy transfers that take

place when a car applies its brakes.

Answer 30

● 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 31

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

Answer 31

The braking force must also be

increased.

Question 32

State two consequences of a vehicle

undergoing very large decelerations.

Answer 32

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