GRAVITATIONAL POTENTIAL ENERGY STORES & KINETIC ENERGY AND ELASTIC ENERGY STORES

Question 1

the kinetic energy store

Answer 1

something that is moving has energy in its kinetic energy store

• the energy an object has because of its motion depends on its mass and speed
• energy transfers to this store when an object speeds up or transferred away from the store when an object slows down

Question 2

what does the energy in a Ek store depend on?

Answer 2

the object’s mass and speed

-the greater the mass the faster it goes, therefore there’s more energy in its Ek energy store

Question 3

Ek = 1/2mv^2

Answer 3

kinetic energy (j) = 1/2 x mass (kg) x speed (m/s)^2

Question 4

what happens when you lift an object in a gravitational field?

Answer 4

this requires work

-some of your muscles transfer energy to the chemical energy store in the muscle to the gravitational potential energy store of the raised object

Question 5

what does the amount of energy in a Ep store depend on?

Answer 5

it depends on the object’s mass, height and the strength of the gravitational field the object is in

Question 6

what happens when something falls?

Answer 6

the energy from its Ep store is transferred to its Ek store

Question 7

Ep = mgh

Answer 7

Ep (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

Question 8

what happens to falling object when there’s no air resistance?

Answer 8

energy is lost from the Ep store and energy is gained in the Ek store

Question 9

what happens in real life when air resistance acts against all falling objects?

Answer 9

it causes some energy to be transferred to other energy stores (the thermal energy stores of the object and surroundings)

Question 10

what happens to an object when it’s stretched or squashed?

Answer 10

it transfers energy to its elastic energy store

Question 11

Ee = 1/2ke^2

Answer 11

elastic potential energy (J) = 1/2 x spring constant(N/M) x extension (M)

Question 12

∆Ep = mg∆h

Answer 12

change of gravitational energy store(J)=mass(kg) x gravitational field strength(N/kg) x change of height(m)

Question 13

change in object’s gravitational potential energy store(J) =

Answer 13

weight(N) x change of height(m)

Question 14

the work done when a object moves up or down depends on:

Answer 14

• how far it’s moved vertically (change of height)

- its weight

Question 15

what is equal/opposite to the force needed to lift an object at constant velocity?

Answer 15

the gravitational force on the object

Question 16

why can objects be lifted easily on the moon?

Answer 16

the gravitational field strength on the moon’s surface is only about 1/6 of the gravitational field strength on the Earth’s surface

Question 17

to calculate the change in gravitational potential energy store of objects going up a slope the

Answer 17

vertical height gained needs to be calculated not the distance along the slope

Question 18

investigating the change of gravitational potential energy store

Answer 18

• measure your mass in kgs using floor scales
• step on and off a sturdy box or low platform
• use the equation to calculate the energy transferred to your gravitational potential energy store when you stepped on the box
  safety: make sure the box is secure and that you feel comfortable to do this

Question 19

what happens when an object is moved upwards?

Answer 19

the energy in it’s Ep store increases, which is equal to the work done on it by the lifting force to overcome the gravitational force on the object

Question 20

what happens when an object is moved downwards?

Answer 20

the energy in it’s Ep store decreases, which is equal to the work done by the gravitational force acting on it

Question 21

investigating kinetic energy stores

Answer 21

• a ball is released on a slope from a measured height above the base of the slope
• calculate the decrease in its Ep store
• due to conservation of energy, this decrease in the Ep store is matched by an equal increase in its Ek store

Question 22

Hooke’s Law

Answer 22

F = ke

Question 23

what happens when the F is increased?

Answer 23

the extension e is increased

Question 24

whats the average force when the spring is extended to extension?

Answer 24

e is 1/2 F, where F = ke
-therefore, the energy stored in the spring = work done = average force extension = 1/2 F
e = 1/2ke^2

Question 25

investigating a catapult

Answer 25

• use a rubber bands to catapult a trolley along a horizontal runway
• the speed depends on how much the catapult is pulled back before the trolley is is released

safety: make sure you do this safely
- protect your hands and feet, and the bench from falling trolleys

Question 26

why is the height drop directly proportional to the speed squared?

Answer 26

the height drop is a measure of the Ek energy store which is directly proportional to the square of its speed