energy and joules?

Question

Energy may be defined as:
A the ability to do work
B the product of power and time
C something which can be transferred from one object to another
D all of the above

How much energy is a 75 Watt light bulb transferring if it is on for 90 seconds?
A 1.2 Joules
B 15 Joules
C 165 Joules
D 6750 Joules

How much time is a 100-Watt light bulb turned "on" if it transfers a total of 7000 Joules of energy?
A 70 seconds
B 6900 seconds
C 7100 seconds
D 700,000 seconds

How much power has a lawnmower delivered if it imparts 6000 Joules of energy in 20 seconds?
A 300 Watts
B 5880 Watts
C 6020 Watts
D 120,000 Watts

Answer 1

1. D, due to basic properties and facts about energy. In particular, you will use answer B to answer the other three questions. Remember, energy is the product of power and time.

2. D, because E = Pt = (75 W)(90 s) = 6750 J

3. A, because t = E/P = (7000 J) / (100 W) = 70 s

4. A, because P = E/t = (6000 J) / (20 s) = 300 W

Answer 2

1. d
2. 75 * 90 = 6750. d
3. 7000/100 = 70 s. a
4 6000/20 = 300. A