P2 3 Energy And Momentum

Question 0

What is the equation for work done?

Answer 0

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

Question 1

When is work done on an object?

Answer 1

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

Question 2

What is work done to overcome friction transferred as?

Answer 2

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

Question 3

What is energy transferred the same as?

Answer 3

Work done.

Question 4

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

Answer 4

• The weight of the object

* How far the object moves vertically

Question 5

When does the gravitational potential energy of an object increase?

Answer 5

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

Question 6

What is the change of gravitational potential energy equation?

Answer 6

The change of gravitational potential energy (J) = its weight (N) x its change of height (m).

Question 7

What is gravitational potential energy?

Answer 7

Gravitational potential energy is energy stored in an object because of its position in the earth’s gravitational field.

Question 8

What does the kinetic energy of an object depend on?

Answer 8

The object’s mass and the object’s speed.

Question 9

What is the kinetic energy equation?

Answer 9

Kinetic energy (J) = 0.5 x mass (kg) x speed^2 (m/s^2).

Question 10

What is KERS (kinetic energy recovery systems)?

Answer 10

KERS store energy when a vehicle brakes and it uses the energy later. Kinetic energy can be transferred to a flywheel for use in braking or overtaking.

Question 11

What is elastic potential energy?

Answer 11

Elastic potential energy is the energy stored in an elastic object when work is done on it to change its shape.

Question 12

What is momentum?

Answer 12

Momentum (kg m/s) = mass (kg) x velocity (m/s).

Question 13

What does the law of conservation of momentum state?

Answer 13

The law of conservation of momentum states that in a closed system, the total momentum before an event is equal to the momentum after the event.

Momentum is conserved in any collision or explosion provided that no external forces act on the objects.

Question 14

What happens to the movement of two objects when they push each-other apart?

Answer 14

• They move apart with different speeds if they have unequal masses
• They move apart with equal and opposite momentum so their total momentum is zero

Question 15

Conservation of momentum in recoil situations:

Answer 15

(Mass of A x velocity of A) + (mass of B x velocity of B) = 0.

Momentum = 0 as both objects were at rest.

Rearrange the equation to give:
(Mass of A x velocity of A) = - (mass of B x velocity of B).

Question 16

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

Answer 16

• The mass of the vehicles
• The change of velocity of the vehicles
• The duration of the impact

Question 17

Fill in the gap:

The longer the impact time is, the … the impact force is reduced.

Answer 17

More.

Question 18

Name some car safety features and their benefits:

Answer 18

• Air bags. In a car crash, an inflated air bag spreads the force of an impact across the upper part of the body. The impact time is also increased, so the effect of the force is lessened.
• Seat belt. The impact time is increased so the decelerating force is reduced by wearing a seat belt. The seat belt also spreads the force across the chest.
• Crumple zones. Crumple zones are designed to ‘give way’ in an impact so the impact time is increased.