Physics Unit 2 - Section 3: Work, energy and momentum 3.0 / 5 based on 1 rating ? PhysicsForces and MotionGCSEAQA Created by: CatherineCreated on: 21-05-13 16:22 What do we mean by the word work? When an object is moved by a force, we say work has been done on that object. 1 of 23 What is the relationship between work and energy? Energy transferred = work done 2 of 23 How do we calculate the work done by a force? work done (J) = force applied(N) x distance moved in the direction of the force (m) 3 of 23 What happens to the the work done to overcome friction? Transfers as energy that heats the objects that rub together and the surroundings. 4 of 23 What does the gravitational potential energy depend on? On the weight of an object and how far vertically it moves. 5 of 23 What happens to the gravitational potential energy of an object when it is...moved up? It increase. The increase is equal to the work done by the lifting force. 6 of 23 ...it moves down? It decreases. The decrease is equal to the work done by the force of gravity on it. 7 of 23 How can we calculate the change of gravitational potential energy when it moves up or down? The change of gravitational potential energy of an object is equal to; its mass x the gravitational field strength x change of height 8 of 23 What does the kinetic energy of an object depend on? On an objects mass and speed 9 of 23 How can we calculate kinetic energy? Kinetic energy (J) = 1/2 x mass (Kg) x speed^2 (m/s)^2 10 of 23 What is elastic potential energy? The energy stored in an elastic object when work is done on an object. 11 of 23 How can we calculate momentum? momentum = mass x velocity 12 of 23 What is the unit for momentum? Kg m/s 13 of 23 What happens to the total momentum of two objects if they collide? Momentum is conserved whenever objects interact, providing the objects are in a closed system so that no external forces act on them. 14 of 23 Why does momentum have a direction as well as size? As it is mass x velocity and velocity is a certain direction. 15 of 23 When two objects push each other apart ... do they move away at different speeds? When two objects push each other apart, they move apart... with different speed if they have unequal masses. 16 of 23 ...why is their total momentum zero? ... with equal and opposite momentum so their total momentum is zero. 17 of 23 When vehicles collide, what does the force of the impact depend on? On mass, change of velocity, and the duration of the impact. 18 of 23 How does the impact of the force depend on the impact force? The longer the impact time, the more the impact force is reduced 19 of 23 What can we say about the impact forces and the total momentum when two vehicles collide? They exert equal and opposite forces on each other and their total momentum is unchanged. 20 of 23 Why do seatbelts and airbags reduce the force on people in car accidents? They spread the force across the chest and they also incrase the impact time. 21 of 23 How do side impact bars and crumple zones work? They 'give way' in an impact, increasing the impact time. 22 of 23 How can we work out if a car in a crash was speeding? We can use the conservation of momentum to find the speed of the car before impact. 23 of 23
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