Smart Teach P2 Foundation Topic 3 In this session, we will cover: Energy Momentum Stopping Distance

Work Done ‘Work done’ is when a force is used to move an object. work done (J) = force x distance. Work done is always measured in Joules (J). Also, work done (J)= energy transferred (J) You will not be asked to rearrange the equation.

Exam examples The weight of the egg is 0.6 N. Calculate the work done on the egg to lift it up by 20 m. State the unit. (3) work done on egg = unit

Exam examples-Look how similar they are! Work Done (J)= Force (N) x Distance (m) Q1. The brakes exert a force of 2000 N. A car takes 9 m to stop after the driver applies the brakes. Calculate how much work is done by this force. (2) Q2. The braking force on another car is 600 N. The force acts for a distance of 15 m. Calculate the work done by the braking force. (2) Q3. A car engine produces an average driving force of 1200 N. The car travels 8.0 m. Calculate the work done by the force over this distance. (2)

Q1 Q2 Q3

Types of energy: Kinetic-When an object is moving Potential-When an object is moved against gravity, i.e. being held above the ground

How to work out the Kinetic Energy of an object Kinetic energy = 1/2 x mass x speed 2 Exam example: The car has a mass of 1400 kg and travels at a velocity of 25 m/s. Calculate the kinetic energy of the car.

Exam example: The car has a mass of 1400 kg and travels at a velocity of 25 m/s. Calculate the kinetic energy of the car.

Exam example: A student stands on the ground with an egg in his hand. He throws the egg vertically upwards. The egg rises to a height of 10 m. Then the egg falls and lands on the ground. Describe the energy changes of the egg during this sequence of events. (6)

Throwing egg up Kinetic energy changes into Potential energy At the top the egg has Potential energy (stopped moving) As it falls, the potential energy changes into kinetic energy

Exam model answer=6 marks Kinetic energy is transferred into potential energy as the egg rises. This then changes back into kinetic energy as it falls back down. Mark scheme ‘a detailed description of a sequence of relevant energy changes or transfers’

Momentum A moving object has momentum. This is the tendency of the object to keep moving in the same direction. Momentum is a vector quantity as it has both a force and a direction. momentum (kg m/s) = mass (kg) × velocity (m/s) A heavy object going very fast will have a large momentum

Q1. The photograph shows a man dropping an egg inside a padded box from a height. He is investigating to see if the padding stops the egg from breaking. The velocity of the container was 18 m/s as it hit the floor. The mass of the container was 0.5 kg. Calculate the momentum of the container. (1) momentum (kg m/s) = mass (kg) × velocity (m/s) units = kg m/s

Your go... Q1. The velocity of the aircraft when it lands is 75 m/s. The mass of the aircraft is kg. Calculate the momentum of the aircraft.(2) momentum = kg m/s Q2. A car has a mass of 800 kg. It has a velocity of 3.0 m/s. Calculate the momentum of the car. (2) momentum of car = kg m/s

Q1 Q2

If momentum changes quickly, there will be a large force on the object. This happens in car crashes. The longer it takes for momentum to change, the less force there is on the object. What about when momentum changes?

How is this knowledge tested in the exam? Q. A pilot begins to land an aircraft. When the aircraft lands, the momentum of each passenger also changes. Explain why it is more comfortable for a passenger if the aircraft takes a longer time to slow down. Model answer: There will be less force on the passenger because the change in momentum is slower

Stopping Distance You may be tested on: -Factors that affect thinking distance or braking distance -Ability to read stopping distance graphs Thinking distance + Braking distance = Stopping Distance

Which of these situations can increase the reaction time of a driver? They are asking, which ones make your reactions slower A an icy road B worn tyres on his car C stopping for a cup of coffee D driving for a long time without taking a break Thinking distance is affected by reaction time. REALLY IMPORTANT!!!! Increasing the reaction time means the time to react is longer, so the reactions are slower! Do not get this confused

How is your knowledge assessed? As speed increases, stopping distance increases.

The chart shows the thinking, braking and stopping distances for an average car and driver stopping from 50 miles per hour as shown in the Highway Code. It also shows the thinking, braking and stopping distances for drivers of cars A and B, both stopping from 50 miles per hour. A and B are different cars on different roads. Use the factors that can affect thinking and braking distances to explain the differences in stopping distances for cars A and B. (6)