Work And Energy

Question 1

When a force acts on a moving body, what happens to energy? (2)

Answer 1

It is transferred, but the total amount of energy remains constant.

Question 2

What is the equation for work done?

Answer 2

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

Question 3

What is work a measure of? (2)

Answer 3

The energy transfer. Work = energy transfer (in the absence of thermal transfer)

Question 4

Has work been done if there is no motion in the direction of the force?

Answer 4

No (unless it is a resistive force such as friction that acts in the opposite direction to movement)

Question 5

What energy is possessed by an object in motion?

Answer 5

Kinetic

Question 6

How does an object posses gravitational potential energy?

Answer 6

Because of its position

Question 7

What energy does an object possess because of deformation?

Answer 7

Elastic energy

Question 8

Equation for kinetic energy?

Answer 8

KE (J) = 1/2 x mass (kg) x velocity*squared (m/s)

Question 9

Equation for gravitational potential energy?

Answer 9

PE = mass (kg) x gravitational field strength (n/kg)or(m/s2) x change in height (m)

Question 10

What is the relationship between force and extension for a spring?

Answer 10

force (N) = spring constant (N/m) x extension (m),
F =kx

Question 11

How do you calculate the work done in stretching a spring using a graph?

Answer 11

Find the area under the force extension graph (W=1/2Fx for a linear relationship

Question 12

How do you calculate the extensions of a spring?

Answer 12

The final length of the spring - the initial length of the spring

Question 13

How can energy efficiency of vehicles be improved? (4)

Answer 13

by:
- reducing aerodynamic losses/air resistance
- reducing rolling resistance
- idling losses
- inertial losses

Question 14

How can aerodynamic losses/air resistance be reduced in vehicles?

Answer 14

more streamlined designs.

Question 15

How can rolling resistance be reduced in vehicles? (2)

Answer 15

having correctly inflated tyres and using materials which don’t heat up as much as they are squashed.

Question 16

How can idling losses be reduced in vehicles?

Answer 16

by using stop - start systems

Question 17

How can inertial losses be reduced in vehicles?

Answer 17

by having lighter cars.

Question 18

why is it important to improve the efficiency of vehicles (2)?

Answer 18

• so less energy is used for a journey to reduce the cost
• to use less energy so that less fossil fuels are burned for energy, improving the environment

Question 19

when is the force applied to a spring not directly proportional to the extension of a spring?

Answer 19

After the elastic limit has been exceeded.

Question 20

What safety features are present in cars? (2)

Answer 20

• airbags
• crumple zones

Question 21

How does an airbag make a person safer in the event of a head-on collision? (6)

Answer 21

• It deploys in front and to the sides of a passenger during a collision
• to increase the distance that the occupant travels before coming to a rest
• The kinetic energy of the occupant is reduced to zero by work being done on the person
• Work is the product of force and distance,
• so by increasing the stopping distance, the force is reduced
• This results in less chance of an injury