Unit 2: 3 - Work, Energy and Momentum Flashcards Preview

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Flashcards in Unit 2: 3 - Work, Energy and Momentum Deck (28)
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0
Q

What is the unit of work?

A

Joules (J)

1
Q

What is work?

A

Work is done when a force moves an object.

2
Q

How do you calculate the amount of work done?

A

Work, W (J) = Force, F (N) * Distance, d, moved in the direction of the force (m).

3
Q

Work done to overcome friction is mainly transferred into energy by ___

A

Heating

4
Q

What is the work done on an object if a force of 300N moves it 8m?

A

2,400J

5
Q

What is gravitational potential energy?

A

Energy stored in an object because of its positioning in the Earth’s gravitational field.

6
Q

What happens to the amount of gravitational potential energy when an object is moved vertically upwards?

A

It gains an amount of GPE equal to the work done on it by the lifting force.

7
Q

What is the formula for finding the change in gravitational potential energy?

A

E subscript p (Ep) = m * g * h

Change in gravitational potential energy, J = mass, kg * gravitational field strength, N/kg * change in height, m

8
Q

What is the increase of Ep when a mass if 40kg is lifted 8m vertically?

A
Ep = m * g * h
Ep = 40 * 9.8 * 8
Ep = 3136J
9
Q

What is power?

A

Power is the rate of energy transfer.

10
Q

What is the formula for power and the unit of measurement?

A

Power, Watts (P) = Energy, Joules (E) / Time, Seconds (t)

P=E/t

11
Q

What energy is always present in moving objects?

A

Kinetic

12
Q

What is the formula for kinetic energy?

A
E subscript k (Ek) = 1/2 m * v^2
Kinetic energy (J) = 1/2 mass (kg) * speed^2 (m/s)
13
Q

A bicycle of mass 20kg moves at a speed of 15m/s. What is its’s kinetic energy?

A
Ek = 1/2 * 20 * 15^2
Ek = 10 * 225
Ek = 2250J
14
Q

What is an elastic object? And how is elastic potential energy generated?

A

An object which retains its shape after being squashed or stretched. When work is done on the object to stretch or squash it, the energy transferred is stored as elastic potential energy.

15
Q

When do objects have momentum?

A

When they are moving.

16
Q

How do we calculate momentum?

A

Momentum, kg m/s (p) = Mass, kg (m) * Velocity, m/s (v)
p=m*v
Note: sometimes momentum may be written in N, it does not matter.

17
Q

What is the momentum of a 1250kg car travelling at 70mph (the national speed limit)?

A

70mph = 112,000 metres an hour.
=31.1 m/s
p = 1250*31.1
p = 38875 kg m/s

18
Q

What is the law of conservation of momentum?

A

Whenever objects interact (collision or explosion), the total momentum after the interaction is equal to the total momentum before it (provided no external forces act upon them).
Basically, the total change of momentum is 0.

19
Q

What is an explosion?

A

When 2 objects move apart with equal and opposite momentum.

20
Q

Give an example of an explosion.

A

A shotgun. The bullet travels in one direction, and the gun recoils in the opposite direction, both with the same momentum.

21
Q

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

A

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

22
Q

When two vehicles collide they exert ____ and their total momentum is ____

A

They exert equal and opposite forces and their total momentum is unchanged.

23
Q

When a force acts upon an object that is able to move, it’s momentum ____

A

Changes

24
Q

If the impact time is short, the forces on the objects are ____.

A

Large.

As the impact time increases, the forces become less.

25
Q

Why do cars have crumple zones?

A

So that the impact time is lengthened, therefore reducing the forces acting upon the passengers inside, increasing the chance of survival.

26
Q

Name 5 safety features of modern cars.

A

Front and rear crumple zones, airbags, collapsible steering wheel, side impact bars (in the doors) and seat belts.

27
Q

Why does a seat belt stretch slightly on impact?

A

To increase the collision time.