Forces and Motion

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

No specific direction is required so it is a scalar quantity

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

• The object has zero displacement

• Displacement is a vector quantity so it also involves direction

• The object starts and ends at the same point

State a typical value for the speed of sound.

330 m/s

What is a typical value for human walking speed?

1.5m/s

What is a typical value for human running speed?

3 m/s

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

• 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

How can speed be calculated from a distance-time graph?

The speed is equal to the gradient of the graph

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

• Drawing a tangent to the curve at required time

• Calculating the gradient of the tangent

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

It is equal to the area under the graph.

What is inertia ?

The tendency of an object to continue in its state of rest or uniform motion.

What is inertial mass?

• a measure of how difficult it is to change a given object’s velocity

• The ratio of force over acceleration

State Newtons third law

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

Give a typical range of values for human reaction time

0.2 Seconds - 0.9 seconds

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

1. Tiredness

2. Drugs

3. Alcohol

Give two factors which may affect braking distance.

1. Adverse (wet/icy) road conditions

2. Poor tyre/brake conditions

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

• work 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

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

The braking force must be increased.

State two consequences of a vehicle undergoing very large decelerations.

1. Kinetic energy converted to heat is very high causing brakes to overheat

2. Loss of control of the vehicle