3 Work, energy and momentum

Question 1

What are the 9 forms of energy?

Answer 1

light
thermal
kinetic
chemical
nuclear
gravitational potential
elastic potential
sound
electrical
(magnetic)

Question 2

What is work?

Answer 2

An object is said to have work done when it transfers energy

Question 3

How do you work out work done?

Answer 3

Work done (joules,J) = force (newtons,N) + distance (metres,M)

Question 4

What is power?

Answer 4

The amount of work done in a given time

Question 5

How do you work out power?

Answer 5

Power (watts,W) = work done (joules,J)
——————————
time (seconds,S)

Question 6

Where is work done to overcome friction mainly transferred?

Answer 6

As energy that heats the objects that rub together and the surroundings

Question 7

Where is gravitational potential energy present?

Answer 7

In any object that is raised above the ground

Question 8

What does gravitational potential energy depend on?

Answer 8

Weight

How far ‘it’ moves vertically

Question 9

When does GPE increase/decrease?

Answer 9

Increase - when the object moves up

Decrease - when the object moves down (towards floor)

Question 10

How do you work out weight?

Answer 10

Mass (kg) x gravity (N/kg)

Question 11

How do you work out work due?

Answer 11

force x distance moved

Question 12

How do you work out change of GPE (J)?

Answer 12

mass (kg) x gravitational field strength (N/kg) x change of height (m)
(weight (N) x change of height (m))

Question 13

What does kinetic energy depend on?

Answer 13

Mass

Speed

Question 14

How do you work out kinetic energy (J)?

Answer 14

1/2 x mass (kg) x speed/velocity2(squared) (m/s2)

Question 15

How do you work out momentum? (kgm/s)

Answer 15

mass (kg) x velocity (m/s)

Question 16

What does the law of conservation of momentum state?

Answer 16

In a closed system, the total momentum before an event and the total momentum after an event are the same/equal

Question 17

What is speed in a certain direction?

Answer 17

velocity

Question 18

What are external forces?

Answer 18

a change in momentum

Question 19

What is force?

Answer 19

the rate of change of momentum

Question 20

What happens when 2 objects push each other apart?

Answer 20

• they move apart with different speeds if they have different masses
• they move apart with equal and opposite momentum so their total momentum is 0

Question 21

When vehicles collide what does the force of impact depend on?

Answer 21

Mass
Change of velocity
Duration of impact

Question 22

Complete this statement:

The longer the impact time is…

Answer 22

the more the impact force is reduced

Question 23

What happens when 2 vehicles collide?

Answer 23

• they exert equal and opposite forces on each other

- their total momentum is unchanged

Question 24

How do seat belts and air bags increase car safety?

Answer 24

Spread the force across the chest and also increases the impact time reducing the force

Question 25

How do side impact bars and crumple zones improve car safety?

Answer 25

they give way in an impact and therefore increase the impact time

Question 26

How can we use the conservation of momentum in car crashes?

Answer 26

To find out the speed of a car before impact