Topic 5- 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 object’s total displacement?

Answer 2

The object has 0 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

Answer 7

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?

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 a 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 from a distance-time graph for an accelerating object?

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

Acceleration (m/s^2) = change in velocity(m/s)/ time taken (s)

Question 12

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

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/s^2

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 Newtons 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 Newtons 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

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

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?

Answer 22

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

Question 23

State Newton’s third law

Answer 23

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

Question 24

What is the stopping distance of a vehicle equal to?

Answer 24

The sum of thinking distance and braking distance

Question 25

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

Answer 25

The stopping distance is increased with an increase in speed

Question 26

Give a typical range of values for human reaction time

Answer 26

0.2 seconds- 0.9 seconds

Question 27

Give three factors which can affect a driver’s reaction time

Answer 27

Tiredness
Drugs
Alcohol

Question 28

Give two factors which may affect braking distance

Answer 28

Adverse (wet/icy) road conditions
Poor tyre/brake conditions

Question 29

Describe the energy transfers that take place when a car applies its brakes

Answer 29

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 30

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

Answer 30

The braking force must also be increased

Question 31

State two consequences of a vehicle undergoing very large decelerations

Answer 31

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