Question
In a small hydroelectric power scheme, 800 kg of water drops through a vertical height of 2.2 m every second. The electrical output is 10.6 kW.
What is the efficiency of the scheme?
A 0.60% B 17% C 60% D 75%
Answer/Explanation
Ans:
C
Question
A man carries 20 tiles from the ground to the roof of a house. Each tile has a mass of $1.2 \mathrm{~kg}$. The roof of the house is $15 \mathrm{~m}$ above the ground.
How much work does the man do against gravity on the tiles in carrying them to the roof?
A $36 \mathrm{~J}$
B $180 \mathrm{~J}$
C $360 \mathrm{~J}$
D $3600 \mathrm{~J}$
Answer/Explanation
Ans:D
Question
A horizontal force pulls a box along a horizontal surface.
The box gains 30 J of kinetic energy and 10 J of thermal energy is produced by the friction between the box and the surface.
How much work is done by the force?
A 10 J
B 20 J
C 30 J
D 40 J
Answer/Explanation
Ans: D
Question
A machine is very efficient.
What does this mean?
A It produces a large amount of power.
B It uses very little energy.
C It wastes very little energy.
D It works very quickly.
Answer/Explanation
Ans: C
Question
A man can either take an escalator or a lift to travel up between two floors in a hotel.
The escalator takes 20 seconds to carry the man between the two floors. The useful work done
against gravity is W. The useful power developed is P.
The lift takes 30 seconds to carry the same man between the same two floors.
How much useful work against gravity is done by the lift, and how much useful power is developed by the lift?
| useful work done against gravity by lift | useful power developed by lift |
A | more than W | less than P |
B | more than W | P |
C | W | less than P |
D | W | P |
Answer/Explanation
Ans: C