# Physics P3

## What is the relationship between initial speed, fi

Average speed (m/s) = (u +v)/ 2

NOTE: use this when the speed is changing uniformly

Distance travelled = (u+v)t/ 2

NOTE: use this when working out instantaneous speed

## What does the gradient of a speed-time graph show?

How fast the object is acclerating.

the area underneath is equal to the distance travelled.

## What does the shape of a speed-time graph show?

the greater the area the faster the speed (greater acceleration)

## What is the significance of positive and negative

Positive acceleration is shown by the graph sloping upwards

Negative acceleration is shown by the graph sloping downwards

## What is the equation for acceleration?

acceleartion (m/S^{2}) = change in speed (or velocity) / time

## What is the relationship between force, mass and a

force = mass x acceleration

## What factors affect thinking distance, breaking di

thinking distance: tired- drugs/alcohol- travelling faster- distraction/lack of concentration

Braking distance: poor road conditions- car is poorley mantained/ speed is increased/ heavy car

Increase in either is unsafe as it increases the chances of an accident

## What is the formula for weight?

weight= mass x gravitational field strength

## What is the formula for power?

power= work done/ time taken

## Apply the equation for kinetic energy

KE (J) = 0.5 mv2

## How do electric power cars cause pollution?

The batteries need reacharging . Recharging uses electricity from a power station. Power station pollute the local atmosphere and cause acid rain.

## What is the relationship between momentum, mass, v

momentum = mass x velocity

force = change in momentum/ time

## Explain how any why crumple zones, seats belts and

-Crumple zones at the front and rear absorb energy by changing shape

-Seat belts stretch a little so some of the person's kinectic energy is converted into elastic energy

-Air bags absorb some of the person's kinetic energy by squashing up around them

## Explain the motion of a falling object in terms of

When the weight of parachutist is greater than the air resistance- the person accelerates

When the two are equal the person reaches a terminal speed

When the air resistance is larger than the parachustist weight the person slows down and the air resistance decreases as they come closer to groun level

## What is the rate of acceleration for an object tha

All objects have the same acceleration point on the Earths surafce.They therefore have the same gravitational potential energy (GPE) which is 10N/kg on Earth.

## use the equation GPE=mgh and interpret examples of

loss of gravitational potential energy (GPE) = gain in kinetic energy (KE)

## How is energy transferred across a roller coaster

electrical energy--> GPE--> kentic energy

If speed doubles KE quadruples

If mass doubles KE doubles

## Explain the realtionship between speed, distance a

Greater distance - higher speed and greater time

Higher speed- Greater distance and shorter time

Greater time- Higher distance and shorter speed

## Interpret distant-time graphs

-the steeper the gradient the higher the speed

-straight lines indicates that the speed is constant

-cruved line shows the speed is changing

## How do you calculate acceleration and distance tra

Gradient of line= acceleration

Distance = the area under a speed-time graph

## What is the formula for acceleration?

acceleartion (m/s2) = change in speed (or velocity) / time taken

## What is the formula for acceleration?

acceleration= force/mass(kg)

## Interpret and explain graphs for thinking and brea

- Thinking distance increases linearly alongside speed so is a straight line

-Breaking distance increases as a squarred relationship so is a curved line

## Explain the derivation of the equation power= forc

power= work done/time taken

=(force x distance)/ time taken

=force x (distance/time)

=force x speed

## Explain kinetic energy in terms of braking distanc

When a car stops its kentic energy changes into heat in the brakes, tyres and road.Therefore when the speed of the car doubles the kentic enrgy and the breaking distance quadruple

Hence why there are speed limits and penalties for drivers who exceed them.

## Explain and evaluate the factors upon which fuel c

-amount of energy required to increase its kinectic energy

-amount of energy required to do work against friction

-speed

-how the car is driven (excessive acceleration and decleration, constant braking and speed changed)

-road conditions such as rough surface

## use Newton's second law of motion to explain relat

If the change in momentum happen in a short time the object will experience large acceleration or deceleration. From Newton's second law of motion this require a large force. This states F= ma

## Evaluate car safety feature

-safety features ansob energy/change shape/ reduce injure by reducing momentum therefore reduce force on the occupants

-problems with seat belts : risk of chest injury, trapped in a fire, drivers encouraged to drive less carefully

## Explain how ABS brakes work

ABS brakes is the primary safety feature to help prevent a crash..

Wheel-seed sensors send information to a computer about the rotational speed of the wheels. The copmuter controls the pressure to the breaks via a pump, to prevent the wheels locking up. This increases the breaking force jsut before the wheels start to skid.

## How do falling objects reach terminal speed?

At first the object accelerates displacing more air particles. This creates greater air resistance so slows down the speed. Therefore ultimately the higher the spped the more air resistance.

When weight becomes equal to air reistance the forces are balanced and there is a costant speed; terminal speed.

## Explain how gravitational field strength varies wi

-GPE varies with postion on the Earths surface 9.78N/kg at the equator and 9.83N/kg at the poles)

-GPE varies with heigh above or depth below the Earth's surface

## What are the energy transfers when an object is fa

as the object falls friction with the air transfers the lost GPE to the surroundings.

the air particles around the object gain internal or thermal energy so increase in temperature

## What equation is used when an object falls due to

mgh = 0.5 mv2

^{ m=mass }

g= acceleration due to gravity

h= height

v= speed

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