Equations and efficiency Flashcards Preview

Year 9 Examinations - Physics > Equations and efficiency > Flashcards

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

5) A wind turbine has an efficiency of 55%. How much energy is required from the wind if the turbine is to generate 750J of electrical energy?

= energy = 55
____ = 0.55
100

Energy = 750
______ = 1363.63
0.55