GPE and KE

What are GPE and KE and how do I use the equations?

Starter: Round the room:

TIME TO BEAT :

Learning outcomes

explain that energy is conserved

describe energy transfers from kinetic to potential and vice versa and calculate the kinetic and potential energy involved

use the equation for kinetic energy

What is gravitational potential energy ?

describe energy transfers from kinetic to potential and vice versa and calculate the kinetic and potential energy involved

Engage brain

If work done = energy transferred what is the equation for working out the gain in GPE?

Tip: check your notes on work done.

GPE

Change in GPE (J) = weight (N) x height (m)

This is the same as Work done (J) = weight (N) x distance (m)

Don’t forget :Weight = mass x gravitational strength (10)

Examples – on earth g = 10 N/Kg

1) If Mia lifts a 100 N box onto a table 2 m high. How much G.P.E. has the box gained?

It’s race time !

Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building? Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building?

Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building?

Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building?

Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building?

Dougie weighs 800N and is standing at the top of a tall building. He has 96000J of G.P.E. How tall is the building?

Danny is on a diet. He runs to the top of 4 flights of stairs 5 times a day. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight?

Danny is on a diet. He runs to the top of 4 flights of stairs 5 times a day. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight? Danny is on a diet. He runs to the top of 4 flights of stairs 5 times a day. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight? Danny is on a diet. He runs to the top of 4 flights of stairs 5 times a day. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight? Danny is on a diet. He runs to the top of 4 flights of stairs 5 times a day. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight? Danny is on a diet. He runs to the top of 4 flights of stairs daily. At the top of the stairs at 70m, he has 59500J of GPE. What is his new weight?

Tom throws his guitar in the air at the end of the concert. It reaches 5m in height. It gains 2500J of GPE at the highest point. What is the mass of the guitar?

Tom throws his guitar in the air at the end of the concert. It reaches 5m in height. It gains 2500J of GPE at the highest point. What is the mass of the guitar?

Tom throws his guitar in the air at the end of the concert. It reaches 5m in height. It gains 2500J of GPE at the highest point. What is the mass of the guitar?

Tom throws his guitar in the air at the end of the concert. It reaches 5m in height. It gains 2500J of GPE at the highest point. What is the mass of the guitar?

Tom throws his guitar in the air at the end of the concert. It reaches 5m in height. It gains 2500J of GPE at the highest point. What is the mass of the guitar?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Harry likes to jump. His best jump is 150 cm. His mass is 75kg. How much GPE does he gain at the highest point of his jump?

Kinetic Energy

• KE (J) = 0.5 x mass x (velocity) 2

use the equation for kinetic energy

The Law of Conservation of Energy

You cannot make or destroy energy. You can only change its type.

explain that energy is conserved

When you lift an object up . . .

. . . you increase its gravitational potential energy.

change in gravitational potential energy= weight vertical height difference

Gravitational potential energy

explain that energy is conserved

If you let the object fall . . .. . . it loses gravitational potential energy . . .. . . and gains kinetic energy.

kinetic energy = ½ mass speed2

Falling

explain that energy is conserved

use the equation for kinetic energy

Lift up a 1 kg bag of flour to a height of 2 m.

change in gravitational potential energy= weight vertical height difference==

Lifting a bag of flour

explain that energy is conserved

As it falls, it loses gravitational potential energy . . .. . . and gains kinetic energy

gain in kinetic energy= loss of gravitational potential energy=

Now drop the bag of flour

explain that energy is conserved

kinetic energy = 20 J ½ mass speed2 = 20 J

What speed does it reach?

explain that energy is conserved

use the equation for kinetic energy

kinetic energy = 20 J ½ mass speed2 = 20 J

mass speed2 = 40

speed2 = 40 (m/s) speed = √40 m/s speed = 6.32 m/s

What speed does it reach?

explain that energy is conserved

use the equation for kinetic energy

Jamaica has a Bobsleigh team Aim: to find out how much speed the Jamaican bobsleigh team reached in their qualifying race.http://www.youtube.com/watch?v=ar4WlU4oQPM

You need to : Work out the GPE, KE and use this to find out the Speed of the bobsleigh.

Info: Height: 121.48mMass: 390 Kg Gravitational Pull : you know that!

explain that energy is conserved

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