A more powerful vehiclewould complete a journey in a shorter time… - Vidyadip

Question

A more powerful vehiclewould complete a journey in a shorter timethan a less powerful one. We talk of the powerof machines like motorbikes and motorcars.The speed with which these vehicles changeenergy or do work is a basis for theirclassification. Power measures the speed ofwork done, that is, how fast or slow work isdone. Power is defined as the rate of doingwork or the rate of transfer of energy. If anagent does a work $W$ in time $t$, then power isgiven by$P$= work/time
$P= W/T$. The unit of power is watt.
(i) The rate of doing work is defined as
$(a)$ Energy
$(b)$ Force
$(c)$ Power
$(d)$ None of these
(ii) Total energy consumed divided by total time taken is called as
$(a)$ Average power
$(b)$ Instantaneous power
$(c)$ Both $a$ and $b$
$(d)$ None of these
(iii) Let A and B having same weight start climbing the rope and reach height of 10m. Let A takes 10sec while B takes 12sec then work done
$(a)$ By both will be same
$(b)$ By $A$ is more than work done by $B$
$(c)$ By $B$ is more than work done by $A$
$(d)$ None of these
(iv) Define 1 Watt of power
(v) An electric bulb of 20W is used for 5h per day. Calculate the ‘units’ of energy consumed in one day by the bulb.

✓

Answer

$(i) c$
$(ii) a$
$(iii) a$
$(iv)$ A power is said to be $1$ watt when $1$ joule of work is done within $1$ second of time.
$(v)$ Power of electric bulb $= 20\ W$
$= 0.02\ kW.$
Time used, $t = 5\ h$
Energy = power $\times $ time taken
$= 0.02kW \times 5 h$
$= 0.10 kW\ h$
$= 0.10$‘units’.
The energy consumed by the bulb $0.10$ units

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