P2 topic 4 Flashcards
what is the stopping distance of a car made up of?
thinking distance and braking distance
thinking distance
the distance travelled by the car as the driver reacts to apply the brakes
braking distance
the distance travelled by the car whilst the brakes are applied before the car comes to a halt
how can thinking distance be calculated?
speed of car x reaction time
how can stopping distance be calculated?
thinking distance + braking distance
what happens to the speed of the car during the thinking distance?
the car continues to move at a constant speed
what increases the thinking distance?
the speed of the car increasing, the driver’a reaction time increasing
when does the driver’s reaction time increase?
when he/she is tired, is under the influence of drugs or alcohol, is distracted (eg by passengers or mobile phones)
when does the braking distance increase?
when the mass of the car increases, when the speed of the car increases
when else does braking distance increase?
when there is reduced friction
how is friction reduced?
it’s reduced between the tyres and roads because of work tyres, between tyres and road because of wet/icy road surface, because of worn brakes
why is friction a nuisance?
it wastes energy
why is friction useful?
it helps us to walk and it also helps vehicles to slow down
how can you reduce the friction between two surfaces?
lubricating them
how can total stopping distance be shown?
on a velocity-time graph
what does the area under a velocity-time graph show?
it’s equal to the distance travelled
what do cars rely on to stop?
friction, created using their brakes
when will the momentum of an object be big?
if the object is travelling quickly and it has a large mass
principle of conservation of momentum
for a system of colliding objects, where there are no external forces, the total momentum before and after the collision remains the sea
how can the impact force on an object be reduced?
by increasing the time taken for the object to stop
what features are there in a car to help reduce the rate of change of momentum on the passengers?
seat belts, crumple zones and air bags
seat belts
stretch slightly during a crash- this increases the time taken for the passenger to stop, reducing impact force to a safe level
crumple zones
cars are designed to crumple- the car, and hence the driver, takes a longer time to stop, reducing the impact force on the driver
air bags
they inflate suddenly during a collision- the stopping time is longer and the impact force on the driver is reduced
what do all moving objects have?
kinetic energy
what is an object’s kinetic energy determined by?
mass and speed
what is KE measured in?
joules
standard measurement for mass
kg
what is potential energy?
stored energy
principle of conservation of energy
energy cannot be created or destroyed, it can simply be transferred from one form to another
what is KE transferred to when a cyclist brakes?
heat in the brakes and sound
what is the energy transfer in a petrol car?
chemical energy of the fuel is changed into KE, heat and sound
what is the energy transfer of a parachutist falling?
their GPE is transformed to KE, hear and a little bit of sound
what is their GPE transferred to as a diver falls off a diving board?
GPE is converted to KE
what does it mean if the braking force and mass of a car are constants?
braking distance is directly proportional to velocity squared- doubling the velocity of the car quadruples the braking distance
when is there work done?
when a force is applied to an object and it moves
what is work done measured in?
Newton metres or joules
what is 1 joule?
the work done when a force of 1 Newton moves through a distance of 1m in the direction of the force
power
the rate at which work is done, or that rate at which energy is transferred
what is 1 watt equal to?
1 joule per second
When is the only time that the equation P=Fv will work?
if the car is travelling at a constant velocity
what do all moving objects have?
momentum
what does a minus sign imply?
an object is moving in the opposite direction- momentum is a vector quantity
principle of conservation momentum
for a system of colliding objects, when there are no external forces, the total momentum before and after the collision remains the same
what happens when objects travelling in different directions collide?
the vector nature of movement before and after a collision must be taken into account
what is an object’s kinetic energy determined by?
its mass and speed/velocity
what is work done by a force equal to?
energy transferred
what is 1 watt equal to?
1 joule per second
