Power

Q.

In a building, there are $15bulbs$ of $45W$, $15bulbs$ of $100W$, $15smallfans$ of $10W$ and $2heaters$ of $1kW$. The voltage of electric main is $220V$. The minimum fuse capacity (rated value) of the building will be approximately:

1. $10A$

2. $20A$

3. $25A$

4. $15A$

Q.

A machine does $1920joule$ of work in $240second$. What is the power of the machine?

Q.

An object does $210J$ of works in $7s$. What is its power?

Q.

What is the SI unit of power?

Q.

A car is moving with a constant speed of $20\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$ against resistance $100N$. The power exerted by the car is

1. $2kW$

2. $5W$

3. $200W$

4. $1kW$

Q.

SI unit of power is:

1. watt

2. joule

3. kilowatt

4. kilojoule

Q. A mass of $10kg$ dropped from a height $50cm$. Find its kinetic energy just before touching ground.

1. $20J$
2. $0J$
3. $5J$
4. $50J$

Q.

Explain the following in terms of joule-

(i) Watt-Hour

Q.

A torch bulb is rated 2.5 V and 750 mA. Calculate (i) its power (in W), (ii) its resistance (in $\Omega$) and (iii) the energy consumed (in J) if this bulb is lighted for four hours.

Q. A jeep carries trailor on a level road at constant speed of $10$ m/sec calculate the power excerted on the trailer if the tension in the coupling is 2000 Newton?

Q.

Express watt-hours in terms of joules.

Q.

Give three differences between work and power.

Q.

If the horse power of an engine $B$ is four times that of the horse power of an engine $A$, then the ratio of the the work done by $A$ and $B$ in the time span of $10min$and $20min$ respectively is _________

1. $1:2$

2. $1:4$

3. $8:1$

4. $1:8$