P1 Kinetic and Potential Energy Stores (page 168)

Question 1

What is the three common ways to calculate energy?

Answer 1

Kinetic
Gravitational Potential
Elastic potential energy store.

Question 2

What is Kinetic Energy Store?

Answer 2

Anything that is moving has energy in its kinetic energy store.

Question 3

How is Kinetic energy transferred to this store, and away?

Answer 3

When an object speeds up, and it is transferred away from this store when an object slows down.

Question 4

What does it mean if the energy in the kinetic energy store depends on the objects mass and speed?

Answer 4

The greater its mass, the faster its going, the more energy there will be in its kinetic energy store.

Question 5

What is the Kinetic formula calculation?

Answer 5

Kinetic energy (j) - Ek = 1/2 mv²

(1/2 mv² means 1/2 x m x v²)
(m means mass(kg), v means speed²)
(m/s)²

see diagram of units on page 168).

Question 6

A car of mass 2500kg is travelling at 20m/s, calculate the energy in its kinetic energy store?

Answer 6

E=1/2 x 2500 x 20² = 500 000)

Question 7

Raised objects store energy in what energy stores?

Answer 7

In gravitational potential energy stores.

Question 8

Lifting an object in a gravitational field requires work, why?

Answer 8

Thes causes a transfer of energy to the gravitational potential energy (g.p.e) store of the raised object. The higher the object is lifted the more energy is transferred to this store.

Question 9

What is the amount of energy in a gravitational potential energy (g.p.e.) store?

Answer 9

This depends on the objects mass, its height and strength of the gravitional field the object is in (see page 202).

Question 10

What is the equation to find the change in energy in an objects gravitational potential energy store for a change in height, h?

Answer 10

Ep- mgh

look at page 168 for explination)

Question 11

Falling objects also transfer what?

Answer 11

Energy

Question 12

When something falls, energy from its gravitational potential energy store is transferred to where?

Answer 12

to its kinetic energy store.

Question 13

What happens for a falling object, when there’s no air resistance?

Answer 13

Energy lost from the g.p.e store - Energy gained in the kinetic energy store.

Question 14

Air resistance (pg 210), acts against all falling objects, why?

Answer 14

it causes some energy to be transferred to other energy stores.

e.g. the thermal energy stores of the object and surroundings

Question 15

Stretching can transfer energy to what stores?

Answer 15

To elastic potential energy stores.

Question 16

Stretching or squashing an object can transfer to what?

Answer 16

It’s elastic potential energy store. (so long as the limit of proportionality has not been exceeded (see page 205), energy in the elastic potential energy store of a stretched spring can be found using:

Elastic potential energy (J) Ee = 1/2ke² (e means extension)² (m)²

(k means spring constant (N/m)

see page 168 for diagram explaination.

Question 17

The energy in an object’s kinetic energy store only changes if?….

Answer 17

it’s changing speed.

(make sure you know how to use the energy equations)

Question 18

A 2.0kg object is dropped from a height from 10m. calculate the speed of the object after it has fallen 5.0m, assuming there is no air resistance. Give your answer to 2 significant figures.

g = 9.8 N/kg (5 marks)

Answer 18

The change in height is 5.0m. so the energy transferred from the gravitational potential energy store is:

Ep = mgh = 2.0 x 9.8 x 5.0 = 98J (1 mark).

This is transferred to the kinetic energy store of te object, so

Ek = 98J (1 mark)

Ek = 1/2mv² so v² = 2Ek ÷ m (1 mark)
= (2 x 98) ÷ 2.0 (1 mark)
= 98 m²/S²
V = square route of 98 = 9.899…
= 9.9 m/s (to 2 s.f.) (1 mark)