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Energy and Momentum.

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Presentation on theme: "Energy and Momentum."— Presentation transcript:

1 Energy and Momentum

2 Energy Property of an object that allows it to do “work”
Measured in Joules(J) kg m2/s2 Mechanical energy is energy due to its position or movement of an object Potential Energy Kinetic Energy Heat from Friction

3 Kinetic Energy, KE Energy of motion

4 Example A 75kg runner is running at a speed of 4m/s. How much kinetic energy does this runner have?

5 Example A car traveling at 20m/s has 240,000J of kinetic energy, what is the mass of the car?

6 Example A 0.05kg ball has a kinetic energy of 2.5J, how fast is the ball moving?

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8 Gravitational Potential Energy, PEg
Stored Energy due to gravitational position above a surface g=10m/s2

9 Example A 5kg box is lifted from the ground up to a 2m shelf. How much did the gravitational potential energy of box increase?

10 Example A 250kg roller coaster car has 87,500J of potential energy at the top of the first hill. How high is the hill?

11 Example What is the mass of an apple that has 2.5J of potential energy when it is 2.5m high in a tree?

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13 Conservation of Energy
Energy can not be created or destroyed Energy can be converted from one form to another

14 Example A 2kg ball at rest at the top of a 16.2m hill rolls down the hill. Assuming no friction, how fast is the ball moving at the bottom of the hill?

15 Example

16 Example A 0.01kg arrow is fired vertically with an initial velocity of 10m/s. Assuming no air resistance, how high did it go?

17 Example A 20kg crate initially at rest at the top of a 4m high ramp slides down to the bottom. At the bottom of the ramp the crate is moving at a speed of 8m/s, how much energy is lost due to friction(EF)?

18 Example

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20 Work Form of energy Force exerted over a distance
Measured in Joules (J)

21 Example A student pushes a cart 4m with a force of 20N. How much work does the student do?

22 Example If a student exerts a 15N force pushing a box, how far do they have to push to do 225J of work?

23 Example A student does 35J of work lifting a book to put it on a shelf 1.75m high. What is the force needed?

24 Example How far does a 2kg rock fall if gravity does 340J of work?

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26 Power Rate at which work is done Rate at which energy is expended
Measured in Watts (W)

27 Example A motor does 50000J of work in 20s. How much power does it develop?

28 Example A student pushes a crate 10m in a time of 4s using a force of 40N. How much power is developed by the student?

29 Example A 50kg cyclist develops 200W of power while pedaling at a speed of 5m/s. What is the average force exerted on the bicycle to maintain this speed?

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31 Momentum Combination of Mass and Velocity Direction is important
Measured in kg*m/s

32 Example A 1200kg car is driving up a 30° incline at a speed of 25m/s. What is the car’s momentum?

33 Example A 75kg runner accelerates from rest until they have a momentum of 600kgm/s. How fast are they running?

34 Conservation of Momentum
Momentum must always be conserved Collisions between objects Projectiles being fired from guns, cannons, etc… Momentum before event must equal momentum after event

35 Example A 0.005kg bullet fired from a gun is traveling at 400m/s. The bullet lodges in a block of wood that was at rest. The mass of the block and bullet together is 2kg. How fast are the block/bullet moving after the bullet lodges in it?

36 Example

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38 Impulse, J Combination of Force and Time Direction is important
Measured in N*s

39 Example A baseball player strikes a ball with a bat with a force of 1000N. If the bat is in contact with the ball for 0.04s, what is the impulse acted on the ball by the bat?

40 Newton’s 2nd Law

41 Impulse-Momentum

42 Impulse - Momentum Impulse equals a change in momentum

43 Example A 0.05kg golf ball at rest is struck by a club with a force of 500N for a duration of 0.005s. What is the speed of the ball after it is hit?

44 Example What force is needed to stop a 1500kg car moving at 29m/s in 0.3s?


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