Power
Category : 9th Class
The rate of doing work is called power.
\[(P)=\frac{\text{work}\,\text{done}\,\text{(W)}}{\text{time}\,\text{taken}\,\text{(t)}}=\,\,\text{or}\,\,P=\frac{W}{t}\]
1 hp = 746 W
= 0.746 kW
Commercial Unit of Energy
The unit joule is too small and hence is inconvenient to express large quantities of energy. So, we use a bigger unit of energy called kilowatt hour (kW h).
1 kW h = 1 kW \[\times \] 1 h
= 1000 W \[\times \] 3600 s
= 3600000 J
1 kW = 3.6 \[\times \] 106 J
Which one of the following is the commercial unit of energy?
(a) Joules
(b) Watt
(c) KW
(d) KWh
(e) None of these
Answer: (d)
One kilowatt hour is equal to:
(a) \[36\times {{10}^{6\,}}J\]
(b) \[136\times {{10}^{6}}J\]
(c) \[3.6\times {{10}^{6}}J\]
(d) \[1.36\times {{10}^{6}}J\]
(e) None of these
Answer: (c)
One horse power is equal to:
(a) 746 watt
(b) 74.6 watt
(c) 7.46 watt
(d) 746 kw
(e) None of these
Answer: (a)
Work done by a string when a stone is tied to it and whriled in a circle is:
(a) Positive
(b) Negative
(c) Zero
(d) All of these
(e) None of these
Answer: (c)
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