Work and energy

Question 1

What is meant by ‘work’?

Answer 1

Work is a measure of the energy transferred.

Question 2

What is ‘work’ measured in?

Answer 2

Joules, J.

Question 3

What is the equation for work done?

Answer 3

work (J) = force x distanced moved in the direction of the force (m). Example, the lifting force of a lifted player is 1000N and the player is lifted 1.5m, the work done is 1500J.

Question 4

What are the exceptions to work done?

Answer 4

It doesn’t take into consideration if no energy is lost as heat to its surroundings (by air resistance or friction).

Question 5

What is gravitational potential energy?

Answer 5

When something is moving vertically, the mass (m) is moved against the Earth’s gravitational field strength (g), through a change in height (h) and it gains potential energy (PE).
Make sure to convert weight to mass if you need to!! Just multiply the weight by 10 to get the mass.

Question 6

What is the equation for gravitational potential energy?

Answer 6

Gravitational potential energy (PE) = mass (m)(kg) x gravitational field strength (g)(N/kg) x change in height (h)(m). or PE=mgh
Or weight x height.
Always use this if the question is about height.

Question 7

What is kinetic energy?

Answer 7

Kinetic energy is movement energy.

Question 8

What is the equation for kinetic energy and when do you use it?

Answer 8

Kinetic energy (J) = 1/2 x mass (m)(kg) x (velocity, v)^2(m/s^2) or KE=1/2mv^2
Always use it when the question mentions speed.

Question 9

What is total energy?

Answer 9

total energy = gravitational potential energy + kinetic energy.
TE = PE+ KE

Question 10

How do springs store energy?

Answer 10

Springs can either get longer or compress. The spring extension depends on the stiffness of the spring (spring constant, k) and the force involved. The force, F (in N), spring constant k (in N/m) and the extension, x (in m) are related together.

Question 11

What is the equation regarding springs and their forces?

Answer 11

force (f) = springs constant (k) x extension (x)

f=kx

Question 12

What is the equation for work done on a spring? (How do you find the work done on a graph?)

Answer 12

w = 1/2Fx

1/2 x area under the graph

Question 13

How can the efficiency of vehicles be maximised?

Answer 13

• Improving aerodynamics / decreases work / decreases fuel/ improving fuel economy / increasing range of vehicle.

Question 14

How can the efficiency of vehicles be maximised? (2)

Answer 14

• Lowering the vehicle / improves aerodynamics / reduces air resistance / improving fuel economy.

Question 15

How can the efficiency of vehicles be maximised? (3)

Answer 15

• Tyres that balance the need for grip (safety) and minimising rolling resistance (decreases fuel consumption).

Question 16

How can the efficiency of vehicles be maximised? (4)

Answer 16

• Reduce energy lost in idle times / temporarily shut down engine / engine used to power small dynamo battery / use to power electrical car systems.

Question 17

How can the efficiency of vehicles be maximised? (5)

Answer 17

• Light weight material instead of heavier / reduces mass of car / reduces inertia to movement / less energy needed to get the vehicle moving in the first place.

Question 18

Name one factor that contributes to the amount of damage done to a car when they crash.

Answer 18

The speed/distance of rapid deaccerleration.

Question 19

What happens if you are in a car that suddenly slows down?

Answer 19

Your motion keeps you moving forward until a force acts to change your velocity (newtons first law) - this could be your head and the wind screen.

Question 20

How do you reduce the force on your body in a car crash?

Answer 20

If you deaccerlerate quickly, there will be a large force on your body. Anything that increases the time taken for the collision, and in doing so reduces the deacceleration, reduces the force acting on you. The car needs to have systems that increase the times for a collision.

Question 21

How do crumple zones help within a collision?

Answer 21

Cars makers design the cars so they will collapse gradually on impact (crumple zones) which significantly increases the time of the collision (reducing the acceleration) and substantially reducing the force on the occupants.

Question 22

What is F=kx the same as?

Answer 22

Y=mx+c

Question 23

In f=kx, what does k do?

Answer 23

K is the gradient (the stiffness of a spring)

Question 24

On a f=kx graph, how do you know if the results are following Hooke’s law?

Answer 24

If the force is directly proportional to the extension. As soon as the line begins to plateu, it no longer follows the rule and the spring risks being unable to reform to its original shape.

Question 25

How do you plot a springs constant graph?

Answer 25

Extension on the x axis, force on the y axis. The gradient is the constant of the spring.

Question 26

What does it mean if the first point on marked on the x axis of a constant graph is above 1?

Answer 26

This graph takes into consideration the springs original length (the original length being the distance between 0 and the first plot point)

Question 27

What does it mean if a spring requires a lot of force to compress or extend?

Answer 27

It should have a very high spring constant.