P2.3

Question 1

What is an elastic body

Answer 1

Objects that return to their original shape when the deforming force is removed.

Question 2

What is a plastic body

Answer 2

Objects that do not return to their original shape when the deforming force is removed.

Question 3

What is Hooke’s law

Answer 3

The extension of a body is directly proportional to the force applied, as long as the limit of proportionality is not exceeded.

Question 4

Hookes law (formula)

Answer 4

F = k x e

Force applied = spring constant X extension

Spring constant - unit N/m

Question 5

How to find spring constant from a force - extension graph

Answer 5

The gradient

Question 6

Where is the limit of proportionality found on a force - extension graph

Answer 6

JUST BEFORE the line starts to curve

Question 7

What is the elastic limit

Answer 7

is the point after which, the body is permanently

deformed when the deforming force is removed.

Question 8

Where is the elastic limit found on a force - extension graph

Answer 8

comes slightly after the limit of proportionality.

Question 9

Does a stiff spring have a large or small spring constant

Answer 9

A large spring constant

= The greater the spring constant, the more force required to extend it per metre, thus the stiffer the spring.

Question 10

Greater the gradient of a force - extension graph

Answer 10

Greater spring constant

Stiffer material

Question 11

Describe the behaviour of an elastic band and copper wire, as they are stretched.

Explain your answer using their force-extension graphs.

Answer 11

ELASTIC BAND
- When the elastic is first stretched, it is quite stiff.
Applying further force causes the elastic to become less stiff.
Finally it becomes stiff again with further force and extension.This is illustrated by the gradient of the F-e graph initially being steep, becoming less steep and then becoming steep again.

Question 12

What is elastic potential energy

Answer 12

energy stored by an elastic body, that has been stretched

Question 13

How does the spring constant effect the EPE of a body

Answer 13

The bigger the spring constant , the stiffer the material, the more force it needs to bring about the same extension… more EPE it has.

Question 14

EPE equation

Answer 14

EPE = ½ x k x e2

Question 15

Weight equation

Answer 15

Weight = mass x gravitational field strength

Question 16

Units of gravitational field strength

Answer 16

N/kg

Question 17

What is gravitational potential energy

Answer 17

the energy stored by a body, whenever it is raised through a height in a planet’s gravitational field.

EXTRA -

This is because in order to lift a body, a force must be applied up to counter its weight.

Thus work is done on the body (energy is transferred to it), where the final energy is in the form of GPE.

Question 18

GPE equation

Answer 18

GPE = m x g x h

Question 19

What is moment (definition)

Answer 19

Moment of a force is a measure of its turning effect.

Question 20

Moment of a force (formula)

Answer 20

Moment = Force x PERPENDICULAR distance

Question 21

Units of moment

Answer 21

Nm

Question 22

How to increase a moment of a force

Answer 22

1. Increasing the size of the force

2. Increasing the perpendicular distance from the pivot

Question 23

When is a body in equilibrium

Answer 23

No resultant force or resultant moment acting upon it

Question 24

What is the principle of moments

Answer 24

The sum of clockwise moments about any point = the sum of anti clockwise moments

Question 25

What is a lever + how do they work

Answer 25

A FORCE MULTIPLER

• A small effort (applied force) on one side of the lever,leads to a large load (force exerted) on a body on the opposite side of the pivot.

Question 26

Mechanical advantage formula

Answer 26

Question 27

Describe and explain how moving the load nearer to the pivot changes the mechanical advantage or a lever

Answer 27

Moving the load closer to the pivot will decrease the perpendicular distance and thus decrease the moment of the load about the pivot. So we need to apply that moment from the left side.

Thus, a smaller effort can be applied to lift the same load as the distance is larger on the left side.

Hence, the mechanical advantage increases.

Question 28

What are gears + how do they work

Answer 28

MOMENT MULTIPLIERS

Force applied between gears is the same,but as ⊥ distance changes, moment of force changes.

Question 29

What happens when you transition from a small gear to a larger gear

Answer 29

Small Gear to Big Gear…… moment increases… larger acceleration(car starting from rest, cycling uphill)

Question 30

What happens when you go from large gear to small gear

Answer 30

Big Gear to Small Gear…… moment decreases… smaller acceleration(car travelling at high speed, cycling on level ground)

Question 31

Suggest and explain which cog on the front wheel you should use to go uphill

Answer 31

You use the smallest cog (12 cm) (1 mark)
because you need a large mechanical advantage. (1 mark)
The force you exert moves the small cog by a larger distance but produces a bigger force that moves a smaller distance. (1 mark)

Question 32

Why do hydraulic machines work

Answer 32

Hydraulics machines only work becauseliquids are incompressible.

As a liquid is incompressible forces are transmitted through them, without loss, in all directions.

Question 33

What does a hydraulic machine do

Answer 33

Hydraulics machines use the pressure exerted in liquids to multiply forces and apply them at a distance.

Question 34

How does a hydraulic machine work

Answer 34

Two pistons are connected by a pipe full of fluid.

A force is applied to piston 1, acts over area 1,and creates a pressure within the fluid.

The same pressure acts at piston 2, over an area 2.

Area 2 > Area 1… output force increased.
Area 2 < Area 2… output force decreased.