Mechanics (AS)

Question 1

I am a quantity with size and direction. What am I?

Answer 1

Vector.

Question 2

I am a quantity with size. What am I?

Answer 2

Scalar.

Question 3

State Newton’s First Law.

Answer 3

The velocity of an object will not change unless a resultant force acts on it.

Question 4

State Newton’s Second Law.

Answer 4

Acceleration is proportional to the force.

F = m x a

Question 5

State Newton’s Third Law.

Answer 5

If an object A exterts a force on object B, then object B exerts an equal but opposite force on object A.

Question 6

Galileo said: all objects fall at the _____ _____.

Answer 6

Galileo said: all objects fall at the (same rate).

A feather takes longer to fall than a brick due to air resistance. In a vaccum, they’d take the same time.

Question 7

When does terminal speed occur?

Answer 7

You will reach a terminal speed when

the friction force = the driving force.

Question 8

What is friction?

Answer 8

Friction is a force that opposes motion.

There are two types of friction:
‘dry friction’ between solid surfaces and
‘fluid friction’ (known as drag, fluid resistance or air resistance).

Question 9

What do frictional forces convert kinetic energy into?

Answer 9

Heat and sound.

Question 10

What is lift?

Answer 10

Lift is an upwards force on an object moving through a fluid.

Question 11

When does lift occur?

Answer 11

Lift occurs when the shape of an object causes the fluid flowing over it to change direction.

Question 12

In which direction does lift act?

Answer 12

The force acts perpendicular to the direction the fluid flows in.

Question 13

What is momentum?

Answer 13

momentum = mass x velocity

p (kg/ms) = m (kg) x v (ms^-1)

Question 14

What is a moment?

Answer 14

A moment is the turning effect of a force.

M = F x d

Where d is the perpendicular distance from the point to the line of action of the force (in m).

Question 15

What is the principle of moments?

Answer 15

For a system to be in equilibrium,

sum of clockwise moments = sum of anticlockwise moments

Question 16

What is a couple?

Answer 16

A couple is a pair of forces of equal size which act parallel to each other, but in opposite directions.

Question 17

A couple is a ______ of forces of equal ______ which act ______ to each other, but in ______ ______.

Answer 17

A couple is a (pair) of forces of equal (size) which act (parallel) to each other, but in (opposite directions).

Question 18

What is the centre of mass?

Answer 18

The centre of mass of an object is the single point that you can consider its whole weight to act through.

Question 19

The centre of mass of an object is the ______ ______ that you can consider its whole ______ to act through.

Answer 19

The centre of mass of an object is the (single point) that you can consider its whole (weight) to act through.

Question 20

How can you find the centre of mass of an irregular object?

Answer 20

1. Hang the object freely from one point.
2. Draw a vertical line downwards.
3. Hang the object from another point.
4. Draw another vertical line downwards.

The centre of mass should be where these lines cross.