Work, energy and momentum

Question 1

W=Fd

Answer 1

work (J) = force (N) x distance moved (m)

Question 2

Friction

Answer 2

Forces opposing the movement of one surface over another

Question 3

Gravitational potential energy

Answer 3

Energy of an object due to its position in a gravitational field

Question 4

E=mgh

Answer 4

energy (J) = mass (kg) x gravitational field strength (N/kg) x change in height (m)

Question 5

Power

Answer 5

The energy transformed or transferred per second (W)

Question 6

P=E/t

Answer 6

power (W) = energy (J) ÷ time (s)

Question 7

E=1/2 mv^2

Answer 7

kinetic energy (J) = 1/2 x mass (kg) x speed squared (m/s)

Question 8

Momentum

Answer 8

Mass times velocity - has a size and a direction

Question 9

p=mv

Answer 9

momentum (kg m/s) = mass (kg) x velocity (m/s)

Question 10

Conversion of momentum

Answer 10

In a closed system, the total momentum before an event is equal to the total momentum after the event

Question 11

Impact time

Answer 11

Time taken for a collision to take place

Question 12

Crumple zone

Answer 12

Region of a vehicle designed to crumple in a collision to reduce the force on the occupants

Question 13

What do we mean by “work” in science?

Answer 13

Work is done on an object when a force makes the energy move

Question 14

What is the relationship between work and energy?

Answer 14

Energy transferred = work done

Question 15

How happens to the work done to overcome friction?

Answer 15

Work done to overcome friction is transferred as energy that heats objects that rub together and the surroundings

Question 16

What does the gravitational potential energy of an object depend on?

Answer 16

The object’s weight and how far it moves vertically

Question 17

What happens to the gravitational potential energy of an object when it moves up or down?

Answer 17

The gravitational potential energy of an object increases when the object goes up and decreases when it goes down

Question 18

What does the kinetic energy of an object depend on?

Answer 18

The kinetic energy of a moving object depends on its mass and its speed

Question 19

What is elastic potential energy?

Answer 19

Elastic potential energy is the energy stored in an object when work is done on the object

Question 20

What is the unit of momentum?

Answer 20

kg m/s

Question 21

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

Answer 21

Momentum is conserved whenever objects interact, provided the objects are in a closed system so that no external forces can act on them

Question 22

What does momentum have a direction as well as a size?

Answer 22

Momentum is mass x velocity, and velocity is speed in a certain direction

Question 23

When two objects push each other apart, how do they move apart?

Answer 23

They move with different speeds if they have unequal mass, and with equal and opposite momentum so that their total momentum is zero

Question 24

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

Answer 24

When vehicles collide, the force of the impact depends on mass, change of velocity and the duration of the impact

Question 25

How does the impact force depend on the impact time?

Answer 25

The longer the impact time is, the more the impact force is reduced

Question 26

What can we say about the impact forces and the total momentum when two vehicles collide?

Answer 26

When two vehicles collide, they exert equal and opposite forces on each other, and their total momentum is unchanged

Question 27

Why do seat belts and air bags reduce the force on people in car accidents?

Answer 27

Seat belts and air bags spread the force across the chest and increase the impact time

Question 28

How do side impact bars and crumple zones work?

Answer 28

Side impact bars and crumple zones “give way” in an impact, so increase the impact time

Question 29

How can we work out if a car in a crash was “speeding”?

Answer 29

We can use the conservation of momentum to find the speed of a car before an impact