Space, time and motion

Question 1

What is the principle of moments?

Answer 1

For an equilibrium of an object, the sum of the clockwise moments about a point must equal the sum of the anti-clockwise moments about the same point

Question 2

What is a forces couple?

Answer 2

Forces that are equal and opposite

Question 3

Define the Newton

Answer 3

When a 1kg mass has an acceleration of 1 ms-2

Question 4

Describe in terms of the forces acting on the driver how wearing a seat belt and having an airbag in a car can help to protect the driver from injury in a head on collision

Answer 4

Prevents the driver from hitting the steering wheel / windscreen

Deflates quickly to prevent whiplash

Increases the time/distance to stop

Decreases the (impact) force on the driver

Much wider area of the bag reduces the pressure

Question 5

State two factors that affect the braking distance of a car. Describe how each factor affects the braking distance

Answer 5

Speed and mass of car

Condition of tyres and brakes

Condition of road, gradient of road

Question 6

State why the equation ‘F = ma’ cannot be applied to particles travelling at speeds very close to the speed of light

Answer 6

The mass of particles increases (at its speed gets closer to the speed of light)

Question 7

How do you find the centre of mass of an unsymmetrical object?

Answer 7

1. suspend object from a point and mark a
   vertical line on the plate
2. Plumb line / ‘pendulum’ (used to find the vertical
   line)
3. Hang from another point and draw
   another vertical line
4. Where the lines intersect gives position of centre
   of gravity

Question 8

Define the torque of a couple

Answer 8

(one of the) force × perpendicular distance between the forces

Question 9

State the principle of conservation of energy

Answer 9

Energy cannot be created or destroyed; it can only be transferred/transformed into other forms