Unit 2: 3 - Work, Energy and Momentum

Question 0

What is the unit of work?

Answer 0

Joules (J)

Question 1

What is work?

Answer 1

Work is done when a force moves an object.

Question 2

How do you calculate the amount of work done?

Answer 2

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

Question 3

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

Answer 3

Heating

Question 4

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

Answer 4

2,400J

Question 5

What is gravitational potential energy?

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

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

Question 8

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

Answer 8

Ep = m * g * h
Ep = 40 * 9.8 * 8
Ep = 3136J

Question 9

What is power?

Answer 9

Power is the rate of energy transfer.

Question 10

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

Answer 10

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

P=E/t

Question 11

What energy is always present in moving objects?

Answer 11

Kinetic

Question 12

What is the formula for kinetic energy?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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.

Question 15

When do objects have momentum?

Answer 15

When they are moving.

Question 16

How do we calculate momentum?

Answer 16

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.

Question 17

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

Answer 17

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

Question 18

What is the law of conservation of momentum?

Answer 18

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.

Question 19

What is an explosion?

Answer 19

When 2 objects move apart with equal and opposite momentum.

Question 20

Give an example of an explosion.

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Changes

Question 24

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

Answer 24

Large.

As the impact time increases, the forces become less.

Question 25

Why do cars have crumple zones?

Answer 25

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

Question 26

Name 5 safety features of modern cars.

Answer 26

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

Question 27

Why does a seat belt stretch slightly on impact?

Answer 27

To increase the collision time.