Flashcards in Equations and efficiency Deck (15):

1

## How do you calculate GPE (gravitational potential energy)?

###
GPE = mass x gravity x

height

Gravity = 9.8

2

##
How do you calculate kinetic energy (KE)?

###
KE= 1/2 x m x v2

M = mass

V2 = velocity squared

3

## How do you calculate velocity?

###
Velocity = distance

__________

Time

4

## How do you calculate work done?

###
W = V x I x T

Workdone x current x time

5

## How do you calculate Specific Heat Capacity (SHC)?

###
SHC = number of joules

____________________

Number of X Number

Kg of mass Of C of temperature

Change

C = E

_____

M x Ø

6

## How do you calculate heat?

###

Heat = mass x SHC x

temperature

E = M x C x Ø

7

## Work done = ...

###
Work done = force x

distance

= (J) x (M)

8

## How do you calculate power (W)?

###
Power = Work

________

Time

W = J

____

S

9

## How do you calculate input energy?

###
= Energy supplied

___________________

Time taken

10

## How do you calculate efficiency?

###
= useful energy

transferred X 100

_________________

Energy supplied

11

##
1) An electric motor is used to raise an object. The object transfers 150J of useful energy when the motor is supplied 250J of electrical energy.

a. What is the total energy supplied to the motor?

b. What is the useful energy that is transferred?

c. What is the efficiency?

###
a. 250J

b. 150J

c. Efficiency = 150

______ X 100

250

= 60%

12

##
2) A filament bulb is supplied with 100J of energy. It wastes 90J as sound and heat energy.

a. What is the total energy supplied?

b. What is the useful energy transferred?

c. What is the efficiency?

###
a. 100J

b. 10J

c. Efficiency = 10

____ x 100

100

= 10%

13

##
3) An electric heater is 90% efficient. If it is supplied with 200J of energy:

a. What is the useful energy that it transfers?

b. For every 200J of energy it is supplied with, how much does it waste?

###
a. = 200 X 90

____________ = 180

100

b. 200 - 180 = 20

14

##
4) A fan is 50% efficient. If it transfers 400J as useful kinetic energy (KE):

a. What is the total energy supplied?

b. How much of the total energy does it waste?

###
a. = 400

______ X 100 = 800

50

b. = 800 - 400 = 400J

15