# P2.3 - Work, Energy & Momentum Flashcards

0
Q

What is the relationship between work and energy?

A

Energy transferred = work done

1
Q

What is “work” in science?

A

Work is done when a force makes an object move.

2
Q

How is the work done by a force calculated?

A

Work done (J) = force (N) x distance in the direction of the force (m)

3
Q

What happens to the work done to overcome friction?

A

The work done is transferred as energy that heats the objects and the surroundings.

4
Q

What does the GPE of an object depend on?

A

Its weight and how far it moves vertically.

5
Q

What happens to the GPE of an object moves up or down?

A

It increases when the object goes up and decreases when the object does down.

6
Q

How is the change in GPE calculated?

A

Mass x gravitational field strength x Δheight

7
Q

Give the equation for change in GPE.

A

Ep = mgh

8
Q

What does the KE of an object depend on?

A

Mass and speed.

9
Q

How is KE calculated?

A

KE (J) = 0.5 x mass (kg) x speed^2 (ms^-1)^2

10
Q

What is elastic potential energy?

A

The energy stored in an elastic object when work is done on the object.

11
Q

How is momentum calculated?

A

Momentum (kgms^-1) = mass (kg) x velocity (ms^-1)

12
Q

What happens to the momentum of two objects when they collide?

A

Momentum is conserved.

13
Q

What does the law of conservation of momentum apply to?

A

A closed system.

14
Q

Why does momentum have a direction as well as size?

A

Velocity is a vector quantity (ie. in a certain direction)

15
Q

When would two objects move at different speeds when pushing away from each other?

A

If the objects have different masses.

16
Q

When two objects push away from each other, why is their total momentum zero?

A

They have equal and opposite momentum.

17
Q

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

A

The mass, change of velocity, duration of the impact.

18
Q

How does the impact force depend on the impact time?

A

The longer the time, the more the force can be reduced.

19
Q

Describe the impact forces and total momentum when two vehicles collide.

A
• They exert equal and opposite forces on each other.

- Their total momentum is unchanged.

20
Q

How are cars designed to lessen force on the passengers?

A

The front and rear of the cars are crumple zones increasing the impact time which reduces the impact force on the car.

21
Q

How does the force of an impact change the momentum of a car?

A
• A front end impact reduces the momentum.

- A rear end impact increases the momentum.

22
Q

Give five features that are designed to improve car safety.

A
• Crumple zones.
• Side impact bars.
• Seat belts.
• Airbags.
• Collapsible steering wheel.
23
Q

Give two design feature benefits of seat belts.

A
• The decelerating force is reduced.

- The force is spread across the chest rather than the head on the windscreen.