Q01: Define “power”
The rate of doing work is defined as
power.
Q02: Explain why power is a useful concept in practical works.
1)
Power is the rate of doing work. (P = W/ t)
2)
The greater the power, the more work it can do in a certain period of
time.
3)
Car engines, water pumps, refrigerators, air conditioners and electric
bulbs, fluorescent tubes, are classified according to their rated powers.
4)
Thus power is a useful concept in practical works.
Q03: Which is more advantageous: to
pay wages according to the amount of work done or according to power?
1) Power can give only the rate of work
done.
2)
The wage depends on amount of work done.
3)
To pay wages according to the amount of work done is more advantageous.
Q04: Since power has only ...(1)... and
no direction, it is a ..(2)... The SI unit for power is ..(3)... The powers of
motors and engines are also expressed in ..(4).. which is a unit in British
engineering system.
(1) magnitude (2) scalar (3)
watt (W) (4) horse power (hp)
Q05: Fill in the blanks. Since power
has only ...(1)... and no direction, it is a ..(2)... The SI unit for power is
..(3)... The powers of motors and engines are also expressed in ..(4).. which
is a unit in British engineering system.
(1) magnitude (2) scalar (3) watt (W) (4)
horse power (hp)
Q06: Why is a high power machine used
to do a lot of work quickly?
1) P = W/ t, where P = power, W = work
done, t = time
2) If work is constant, P µ 1/t
3) If time is small (quick), power must
be large (high power).
Q07(a): When a large
power machine and a small power machine are operated for the same period of
time, will the large power machine consume less fuel?
1) No.
2) P = W/ t, where P = power, W = work
done, t = time
3) If time is constant,
4) If power is large, work done is also
large.
5) To do a larger work, a larger energy
or fuel is needed.
Q07(b): Can a lot of work be done only if a large power machine is
used?
1) No.
2) P = W/ t, where P = power, W = work
done, t = time
3) If work is constant, P µ 1/t
4) If power is small, time must be
large.
5) So a small power machine may be used
for as long as necessary.
Q07(c): A lot of
work can be done by operating a small power machine for as long as necessary.
Why?
1) P = W/ t where P = power, W = work done, t = time
2) If work is constant, P µ 1/t
3) If power is small, time must be
large.
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