Calculate the efficiency of a TV which takes in 5000J of energy per second and transfers 1000J as useful light energy and 1500J as useful sound energy. The remaining 2500J is wasted as heat energy. Express your answer as a decimal and not a percentage.
Answers
Answer:
EQUATIONS OF CONSTANT ACCELERATION
Efficiency, Work and power
1) A light bulb takes in 30J of energy per second. It transfers 3J as useful light energy and 27J as heat energy. Calculate the efficiency.
Efficiency as a percentage = 0.1 x 100 = 10%
2) A kettle takes in 2000J of energy per second. It transfers 1500J as useful heat energy and 500J is wasted as sound energy. Calculate the efficiency of the kettle.
Efficiency as a percentage = 0.75 x 100 = 75%
3) Calculate the efficiency of a hair dryer which takes in 3000J of energy per second and transfers 600J as useful heat energy. Express your answer as a decimal and not as a percentage.
4) Calculate the efficiency of a TV which takes in 5000J of energy per second and transfers 1000J as useful light energy and 1500J as useful sound energy. The remaining 2500J is wasted as heat energy. Express your answer as a decimal and not a percentage.
5) Calculate the efficiency of a light bulb that gives of 40J of light from 200J of electrical energy.
Efficiency as a percentage = 0.2 x 100 = 20%
6) Calculate the efficiency of a radio that gives of 30J of sound from 360J of electrical energy.
Efficiency as a percentage = 0.083 x 100 = 8.3%
7) Calculate the efficiency of a runner who produces of 500J of kinetic energy from 2500J of chemical energy.
Efficiency as a percentage = 0.2 x 100 = 20%
8) Calculate the percentage efficiency of a student who takes 2 hours to do 30 minutes of homework.
Efficiency as a percentage = 0.25 x 100 = 25%
9) What is the useful light output from a bulb of efficiency 0.25 when supplied with 600J of energy?
10) What is the useful work output from a motor of efficiency 0.60 when supplied with 1200J of energy?
11) What is the useful sound output from a radio of efficiency 50% when supplied with 20J of energy?
12) What is the useful work done by a runner of efficiency 0.30 when supplied with 200J of energy?
13) How long does it take a student of efficiency 40% to do a 30 minute homework?
14) A light bulb is rated as 40W
a. How much electrical energy does this bulb use in one second?
40W
b. Calculate the efficiency of the bulb if it gives out 5J of light in one second.
remember 40W = 40 J/s
c. What is the percentage efficiency of the bulb?
0.125 x 100 = 12.5%
d. What is the useful power output of the light bulb?
5W
e. How much light energy should the bulb give out in 3 minutes?
5W x (3 x 60) = 900J
f. How much heat energy should the bulb give out in 3 minutes?
Heat energy / sec = 40W 5W = 35W
35W x 180 = 6300W (6.3kW)
15) An electric motor pulls a mass of 4kg up by 3 metres in 5 seconds when supplied with 360J of electrical energy.
a. What is the weight of the mass?
W = mg = 4 x 10 = 40N
b. How much work does the motor do?
Work = force x distance = 40 x 3 = 120J
c. What is the power of the motor?
Power = work / time = 120 / 5 = 24W
d. What is the percentage efficiency of the motor?
Efficiency as a percentage = 0.33 x 100 = 33.3%
e. What is the power supplied to the motor?
Power = energy supplied / time = 360 / 5 = 72W
16) A runner of mass 120kg maintains a speed of 5 m/s while using chemical energy from food at a rate of 4500J per second. Calculate:
a. The runners kinetic energy
KE = 1500J
b. The input power to the runner from food
Power = 4500 J/s = 4500W
c. The efficiency of the runner
Answer:
the efficiency of a TV which takes in 5000J of energy per second and transfers 1000J as useful light energy and 1500J as useful sound energy. The remaining 2500J is wasted as heat energy.
input = 5000 J
favourable output = 1000 + 1500 = 2500 J
efficiency,