P2.3 - Work, Energy & Momentum

Question 0

What is the relationship between work and energy?

Answer 0

Energy transferred = work done

Question 1

What is “work” in science?

Answer 1

Work is done when a force makes an object move.

Question 2

How is the work done by a force calculated?

Answer 2

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

Question 3

What happens to the work done to overcome friction?

Answer 3

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

Question 4

What does the GPE of an object depend on?

Answer 4

Its weight and how far it moves vertically.

Question 5

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

Answer 5

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

Question 6

How is the change in GPE calculated?

Answer 6

Mass x gravitational field strength x Δheight

Question 7

Give the equation for change in GPE.

Answer 7

Ep = mgh

Question 8

What does the KE of an object depend on?

Answer 8

Mass and speed.

Question 9

How is KE calculated?

Answer 9

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

Question 10

What is elastic potential energy?

Answer 10

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

Question 11

How is momentum calculated?

Answer 11

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

Question 12

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

Answer 12

Momentum is conserved.

Question 13

What does the law of conservation of momentum apply to?

Answer 13

A closed system.

Question 14

Why does momentum have a direction as well as size?

Answer 14

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

Question 15

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

Answer 15

If the objects have different masses.

Question 16

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

Answer 16

They have equal and opposite momentum.

Question 17

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

Answer 17

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

Question 18

How does the impact force depend on the impact time?

Answer 18

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

Question 19

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

Answer 19

• They exert equal and opposite forces on each other.

- Their total momentum is unchanged.

Question 20

How are cars designed to lessen force on the passengers?

Answer 20

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

Question 21

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

Answer 21

• A front end impact reduces the momentum.

- A rear end impact increases the momentum.

Question 22

Give five features that are designed to improve car safety.

Answer 22

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

Question 23

Give two design feature benefits of seat belts.

Answer 23

• The decelerating force is reduced.

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