GPE and KE What are GPE and KE

GPE and KE What are GPE and KE and how do I use the equations? Starter: Round the room: TIME TO BEAT :

Learning outcomes ü explain that energy is conserved ü describe energy transfers from kinetic to potential and vice versa and calculate the kinetic and potential energy involved ü use the equation for kinetic energy

What is gravitational potential energy ? üdescribe 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 800 N and is standing at the top of a tall building. He has 96000 J 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 70 m, he has 59500 J 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 70 m, he has 59500 J of GPE. What is his new weight?

Tom throws his guitar in the air at the end of the concert. It reaches 5 m in height. It gains 2500 J 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 75 kg. How much GPE does he gain at the highest point of his jump?

Kinetic Energy • KE (J) = 0. 5 x mass x (velocity) 2 üuse the equation for kinetic energy

The Law of Conservation of Energy You cannot make or destroy energy. You can only change its type. üexplain that energy is conserved

Gravitational potential energy When you lift an object up. . . you increase its gravitational potential energy. change in gravitational potential energy = weight vertical height difference üexplain that energy is conserved

Falling If you let the object fall. . . it loses gravitational potential energy. . . and gains kinetic energy = ½ mass speed 2 üuse the equation for kinetic energy üexplain that energy is conserved

Lifting a bag of flour Lift up a 1 kg bag of flour to a height of 2 m. change in gravitational potential energy = weight vertical height difference = = üexplain that energy is conserved

Now drop the bag of flour As it falls, it loses gravitational potential energy. . . and gains kinetic energy gain in kinetic energy = loss of gravitational potential energy = üexplain that energy is conserved

What speed does it reach? kinetic energy = 20 J ½ mass speed 2 = 20 J üuse the equation for kinetic energy üexplain that energy is conserved

What speed does it reach? kinetic energy = 20 J ½ mass speed 2 speed = 20 J = 40 (m/s) = √ 40 m/s = 6. 32 m/s üuse the equation for kinetic energy üexplain that energy is conserved

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=ar 4 Wl. U 4 o. QPM You need to : Work out the GPE, KE and use this to find out the Speed of the bobsleigh. Info: Height: 121. 48 m Mass: 390 Kg Gravitational Pull : you know that! üexplain that energy is conserved

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