Forces,Motion,Energy and Momentum Revision Mock 2015

Stopping distances   Thinking distance is the distance a car travels before the brakes are applied. Braking distance is the distance a car travels whilst the brakes are being applied. Stopping distance = thinking distance + braking distance Stopping distance Braking distance Thinking distance How far does a vehicle travel before it stops? The stopping distance is the sum of the thinking distance and the braking distance.

Can you match up the words with their definitions? Stopping distance Friction Thinking distance Braking distance One of forces the road exerts on the tyres as the car is stopping. The distance a car travels whilst it is braking. The distance a car travels before the brakes are applied. The sum of thinking distance and the braking distance.

Momentum Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: Momentum = Mass x Velocity (in kgm/s) (in kg) (in m/s) P VM What is the momentum of the following? 1)A 1kg football travelling at 10m/s 2)A 1000kg Ford Capri travelling at 30m/s 3)A 20g pen being thrown across the room at 5m/s 4)A 70kg bungi-jumper falling at 40m/s

10 m/s 60 m/s p = mv p = 1100 x 10 p = kg m/s p = mv p = x 10 p = kg m/s p = mv p = 1100 x 60 p = kg m/s

All moving objects have momentum. This is a measure of how difficult it is to stop a moving object. The momentum of a vehicle depends on its mass and velocity. What is momentum?

All moving objects have momentum. This is a measure of how difficult it is to stop a moving object. The momentum of a vehicle depends on its mass and velocity. What is momentum? (H) change in momentum time When a force is applied to an object, for example if it collides with something, the object’s velocity changes. This means that its momentum will also change. The change in momentum depends on the size of the force and the time for which it is applied. force =

Car crashes and momentum What happens if two cars travelling very quickly collide? Both cars come to a stop in a short space of time. Why could this cause serious injury? A very large change of momentum in a short space of time means the car occupants will experience a very large force. This means they are more likely to get a serious injury.

Car crashes and momentum (H) What happens if two cars travelling very quickly collide? Both cars come to a stop in a short space of time. This means that the cars and their occupants experience a large change of momentum very quickly. Why could this cause serious injury? A very large change of momentum in a short space of time means the car occupants will experience a very large force. This means they are likely to sustain serious injury.

Many car safety features work in one of two ways: Reducing force in car crashes 1. Increasing the amount of time taken for the person to decelerate in a collision. This means that change in momentum occurs over a longer time, so the person experiences a smaller force. How are these principles used by: seatbelts airbags crumple zones? 2. Absorbing some of the vehicle’s kinetic energy by changing shape.

Many car safety features work in one of two ways: Reducing force in car crashes (H) 1. Increasing the amount of time taken for the person to decelerate in a collision. This means that change in momentum occurs over a longer time, so the person experiences a smaller force. How are these principles used by: seatbelts airbags crumple zones? 2. Absorbing some of the vehicle’s kinetic energy by changing shape. This reduces the forces on the occupants.

How do car safety features work?

Increasing collision time calculation A 90 kg driver with no seatbelt crashes at 12.5 m/s, impacting against the steering column in 0.04 seconds. What is the force on the driver? momentum = mass × velocity = 90 × 12.5 = 1125 kg m/s = = 28,125 N force = change in momentum time With a seatbelt, the driver would have stopped in 0.2 seconds. Can you calculate the force on the driver if they’d worn a seatbelt.

Work, force, distance calculations

A cyclist peddles a bicycle with a force of 1,000 N and moves it 250 m. Calculating work done question 1 = 1,000 × 250 = 250,000 J = 250 kJ = force × distance work done How much work has been done by the cyclist?

How is power calculated? The power exerted by an object can be calculated using the equation: Time is measured in seconds (s). Power is measured in watts (W). Work done is measured in joules (J). work done time taken power = Remember that work done = energy transferred, so energy transferred can be used instead of work done in the equation above.

A lawnmower engine does 10 kJ of work in 10 seconds. What is the power of the engine? Calculating power question 1 = 1,000 W = 1 kW power = work done time = 10,000 / 10

When a bungee jumper starts to fall he starts to lose GPE. As the elastic cord pulls the bungee jumper back up, he gains GPE. The gravitational potential energy (GPE) of an object on Earth depends on its mass and its height above the Earth’s surface. What is gravitational potential energy?

How is GPE calculated? The GPE of an object can be calculated using this equation: GPE = mass × gravitational field strength × height Height is measured in metres (m). Mass is measured in kilograms (kg). GPE is measured in joules (j). Gravitational field strength is measured in newtons per kilogram (N/kg), usually taken as 10 N/kg on Earth.

Factors affecting GPE

An osprey with a mass of 2 kg flies at a height of 200 m above the ground. Calculating GPE question 1 How much gravitational potential energy does the osprey have? = 2 × 10 × 200 GPE = mass × gravitational field strength × height = 4,000 J

GPE, mass and height calculations

Kinetic energy is the energy an object has because it is moving. What is kinetic energy? The word ‘kinetic’ comes from the Greek word ‘kinesis’, meaning motion. All moving things have kinetic energy, but the amount of energy they have is not just dependent on how fast they are moving. What other factors affect the kinetic energy of a moving object?

How is kinetic energy calculated? The kinetic energy (KE) of an object can be calculated using this equation: Velocity is measured in metres per second (m/s). Mass is measured in kilograms (kg). KE is measured in joules (j). KE = ½ × mass × velocity 2 = ½mv 2

kinetic energy = ½ × mass × velocity 2 A car with a mass of 1,500 kg travels at a velocity of 20 m/s. Calculating kinetic energy question What is the kinetic energy of the car? = 300,000 J = 300 kJ = ½ × 1,500 × 20 2