Work (oh no, not again
GRAVITATIONAL ENERGY
When we raise an object, the energy we use is changed into gravitational energy. We can use the following formula to work out how much energy has been converted to gravitational energy.
Gravitational energy = mass x gravitational field strength x height = mgh
GPE = mgh
Use this formula to answer the following questions. In all questions, take g = 10 N/kg.
1. If Eloise lifts a mass of 10 kg onto a table 1.25 m high. How much G.P.E. has the mass gained?
2. If Chan climbs a ladder 3.4 m tall, and Chan has a mass of 48 kg, how much G.P.E. has she gained?
3. Calculate the change in gravitational potential energy when:
a) a car of mass 500kg climbs a hill 400m high;
b) a climber of mass 65kg climbs a rock face 200m high;
c) a bird of mass 0.5kg flies from the ground to a height of 500m.
4. A man of mass 80 kg standing at the top of a tall building has 96000 J of G.P.E. How tall is the building?
5. How much G.P.E. would he have if the same building were on the moon? (g = 1.6 N/kg on the moon)
6. A catapult has 20 J of energy to project a marble of mass 0.005 kg upwards. What is the maximum height the marble can reach above the catapult?
7. The water from a hydroelectric power station can release 40 MJ of energy falling through 40 m. What mass of water must be used in this process?
8. A girl (on the earth) drops a ball of mass 0.5 kg from a height of 2 metres.
i. How much G.P.E. does the ball have before it has dropped?
ii. How much G.P.E. does it have just before it hits the ground?
iii. How much kinetic energy does it have just before it hits the ground?
iv. How fast is it moving when it hits the ground?
9. A roman catapult relied on a heavy mass falling onto a pivoted beam, to launch a smaller mass into the air. If a mass of 200kg is allowed to fall 3 m, how much PE did the mass have before it fell? What is the largest mass it could launch over a wall 10 m high if no energy is wasted?
GRAVITATIONAL ENERGY
When we raise an object, the energy we use is changed into gravitational energy. We can use the following formula to work out how much energy has been converted to gravitational energy.
Gravitational energy = mass x gravitational field strength x height = mgh
Ep = mgh
Use this formula to answer the following questions. In all questions, take g = 10 N/kg.
1. If Karol lifts a mass of 10 kg onto a table 1.25 m high. How much G.P.E. has the mass gained?
2. If Angelina climbs a ladder 3.4 m tall, and Angelina has a mass of 48 kg, how much G.P.E. has she gained?
3. A man of mass 80 kg standing at the top of a tall building has 96000 J of G.P.E. How tall is the building? How much G.P.E. would he have if the same building were on the moon? (g = 1.6 N/kg on the moon)
4. A girl (on the earth) drops a ball of mass 0.5 kg from a height of 2 metres.
i. How much G.P.E. does the ball have before it has dropped?
ii. How much G.P.E. does it have just before it hits the ground?
iii. How much kinetic energy does it have just before it hits the ground?
iv. How fast is it moving when it hits the ground?
5. Now write 3 questions of your own about G.P.E. (And answer them!)
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