Work, Energy and Power

Question 1

system

Answer 1

object or group of objects

Question 2

equation for speed

Answer 2

distance / time

v = s/t

Question 3

Scalar quantity

Answer 3

quantity described by magnitude only and no direction

Question 4

Vector quantity

Answer 4

both magnitude and direction must be specified

Question 5

velocity

Answer 5

speed in a given direction

Question 6

displacement

Answer 6

straight line of movement

Question 7

Resultant force

Answer 7

the resultant force is the overall force acting on an object. This is where all the forces can be added together to find one individual force.

Question 8

If an object is in equilibrium

Answer 8

Then the resultant force is zero

Question 9

Newtons first law states:

Answer 9

If forces acting on an object are balanced, than the resultant force on the object is zero. If the object is at rest than it will stay stationary.
If the object is moving, then it will stay moving with the same speed and direction.

Question 10

if an object is balanced:

Answer 10

it will behave as if there is no resultant force acting on it.

Question 11

why could an object be balanced?

Answer 11

all the forces acting on it would cancel each other out

Question 12

why do all objects resist a change in velocity

Answer 12

Because all objects need a force to move in the same direction, go faster or slower, or change direction.

Question 13

equation linking force, mass and acceleration

Answer 13

Force = mass x acceleration

Question 14

Newtons second law

Answer 14

The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.

Question 15

Work done

Answer 15

measure of energy transferred

Work done is defined as the amount of force needed to move an object a certain distance. In essence, it is a measure of an energy transferred to or from an object which allows it to be moved.

Question 16

work done equation

Answer 16

Work done = force x distance

Question 17

Joule definition

Answer 17

The work done when a 1N force acts through a distance of 1 metre

Question 18

equation for kinetic energy

Answer 18

Ek=1/2mv2
Kinetic energy = half x mass x velocity squared

Ek in joules
mass in kg
velocity squared in m/s

Question 19

what happens when a car brakes

Answer 19

work is done by friction between the brakes and the wheel, leading to a transfer of kinetic energy to thermal energy in the brakes.

Question 20

gravitational potential energy equation

Answer 20

Ep = mgh
gravitational potential energy = mass x gravitational field strength x height

Ep in J
mass in kg
gravitational field strength in N/kg
height in m

Question 21

power

Answer 21

rate at which energy is transferred or work is done

Question 22

what happens if the power of a device increases

Answer 22

The more powerful a device is the faster it transfers energy

Question 23

Equation for power

Answer 23

Power (W) = energy transferred (J) / Time (s)

Question 24

What would happen if 2 electric motors lift the same weight through the same height.

Answer 24

The one that lifts it faster has more power

Question 24

What would happen if 2 electric motors lift the same weight through the same height.

Answer 24

The one that lifts it faster has more power

Question 25

Power efficiency equation

Answer 25

Efficiency = Useful power output / Total power input

Question 26

Elastic deformation

Answer 26

object returns to original length when extending force removed

Question 27

Inelastic deformation

Answer 27

object does not return to original length when elastic force removed

Question 28

Hookes Law

Answer 28

spring extension is directly proportional to force applied.

Question 29

Hookes law equation

Answer 29

Force = spring constant x extension

F = Ke
force measured in N
spring constant measured in N/m
Extension measured in M

Question 30

Elastic potential energy equation

Answer 30

Ee=1/2ke^2

Elastic potential energy = 0.5 x spring constant x extension squared

Question 31

What would happen if a force that streches/compresses a string does work and elastic potential energy is stored in the string?

Answer 31

Provided the string is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal