Transcript Gravitational Potential Energy – GPE

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
Gravitational potential energy
When you lift an object up . . .
. . . you increase its gravitational potential energy.
change in gravitational potential energy
= weight  vertical height difference
explain that energy is conserved
Falling
If you let the object fall . . .
. . . it loses gravitational potential energy . . .
. . . and gains kinetic energy.
kinetic energy = ½  mass  speed2
use the equation for kinetic energy
explain 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
=
=
explain 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
=
explain that energy is conserved
What speed does it reach?
kinetic energy = 20 J
½  mass  speed2 = 20 J
use the equation for kinetic energy
explain that energy is conserved
What speed does it reach?
kinetic energy = 20 J
½  mass  speed2
mass  speed2
speed2
speed
speed
= 20 J
= 40
= 40 (m/s)
= √40 m/s
= 6.32 m/s
use the equation for kinetic energy
explain 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=ar4WlU4oQPM
You need to :
Work out the GPE, KE and use this to find out the Speed of the
bobsleigh.
Info:
Height: 121.48m
Mass: 390 Kg
Gravitational Pull : you know that!
explain that energy is conserved
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