# Average and Instaneous Power

## Trending Questions

**Q.**Convert 1 kilowatt hour into joule.

**Q.**

What is the relationship between power, force and velocity?

**Q.**

The power of a pump, which can pump 200kg of water to a height of 200m in 10sec is (g=10m/s−2)

400

*kW*960

*kW*40

*kW*80

*kW*

**Q.**

When a constant force is applied to a body moving with a constant acceleration, is power of the force constant? If not, how will force vary with speed for the power to be constant?

**Q.**

Calculate the power of an electric pump in horsepower with can lift $2000{m}^{3}$ of water from a depth of $20m$ in $25min$.($1{m}^{3}$ of water=${10}^{3}kg$, g=$10m/{s}^{2}$)

[$1HP=750watts$]

**Q.**The transformer ratio in the step-up transformer is

- equal to 1.
- greater than 1.
- less than 1.
- less than 0.

**Q.**

The machine gun fires $240$ bullets per minute. If the mass of each bullet is $10g$and the velocity of the bullets is$600m{s}^{-1}$ , the power (in kW) of the gun is

$43200$

$432$

$72$

$7.2$

**Q.**Water falls from a height of 80 m at the rate of 20 kg/s to operate a turbine. The losses due to frictional force are 20 % of the energy. How much power is generated by the turbine? (g=10 ms2)

- 7.0 kW
- 12.3 kW
- 12.8 kW
- 10.2 kW

**Q.**If a force →F =(7 ^i−6 ^j+2 ^k) N and velocity →v=(6 ^i+^k) m/s, then the instantaneous power is

- 42 watts
- 46 watts
- 44 watts
- 57 watts

**Q.**

In a hydroelectric power station, the height of the dam is 10 m. How many kg of water must fall per second on the blades of a turbine in order to generate 1 MW of electrical power? Take g=10 ms−2.

104 kgs−1

105 kgs−1

106 kgs−1

103 kgs−1

**Q.**An engine pumps up 100 kg of water through a height of 10 m in 5 s. Given that the efficiency of the engine is 60%, what is the power of the engine? (Take g=10 m/s2)

- 33 kW
- 3.3 kW
- 0.33 kW
- 0.033 kW

**Q.**If the force →F=(60^i+15^j−3^k) N and velocity →v=(2^i−4^j+5^k) m/s, then instantaneous power is

- 195 watt
- 45 watt
- 75 watt
- 100 watt

**Q.**Power versus time graph for a force is given below. Work done by the force upto time t (≤t0),

- First decreases then increases
- Always increases
- First increases then decreases
- Always decreases

**Q.**

A family uses 8 kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW? (b) Compare this

area to that of the roof of a typical house.

**Q.**A block of mass m is located on a horizontal plane. The block acquires a horizontal velocity v0 due to friction. Find the mean power developed by the friction force during the motion of the body. The frictional cofficient is μ=0.3, m=2 kg and v0=5 m/s (Take g=10 m/s2)

- 30 watt
- 45 watt
- 60 watt
- 15 watt

**Q.**A pump is required to lift 800 kg of water per minute from a 10 m deep well and eject it with speed of 20 m/s. The power required (in watts) of the pump will be

(Take g=10 m/s2)

- 5000
- 8000
- 6000
- 4000

**Q.**Power versus time graph for a force is given below. Then, work done by the force upto time t (≤t0)

- first decreases then increases
- first increases then decreases
- always increases
- always decreases

**Q.**

Define watt. Express kilowatt in terms of joule per second. A 150 kg car engine develops 500 W for each kg. What force does it exert in moving the car at a speed of $20m{s}^{-1}?$

**Q.**Solar insolation of a rectangular module (1.5 m×2.0 m) of a solar cell is 550 W/m2. If efficiency of the cell is 12 %, what power can be drawn from cell?

- 396 W
- 240 W
- 99 W
- 198 W

**Q.**

A bulb is rated $100W-240V$. What is the magnitude of current drawn by the bulb?

**Q.**A particle of mass m moves along a circle of radius R with a normal acceleration varying with time as an=bt2, where b is a constant. Find the mean value of power averaged over the first 2 seconds after the beginning of motion. (m=1, b=2, R=1)

**Q.**An object of mass m, initially at rest under the action of a constant force F attains a velocity v in time t. Then, the average power supplied to mass is

- mv22t
- Fv2
- Both a and b are correct
- Both a and b are wrong

**Q.**

A body does $50J$ of work in $5seconds$. What is its power?

**Q.**

The average power dissipation in pure inductance is:

zero

**Q.**A body of mass 1 kg begins to move under the action of a time dependent force →F=(2t^i+3t2^j) N. Calculate the instantaneous power developed at time t ?

- (2t3+3t4) W
- (2t3+3t5) W
- (2t2+4t4) W
- (2t2+3t3) W

**Q.**

An unruly demonstrator lifts a stone of mass 200 g from the ground and throws it at his opponent. At the time of projection, the stone is 150 cm above the ground and has a speed of 3.00 m/s. Calculate the work done by the demonstrator during the process. If it takes one second for the demonstrator to lift the stone and throw, what horsepower does he use ?

**Q.**

What is the efficiency formula?

**Q.**A force (2^i+3^j+^k) N acting on a body, displaces it from →r1=(2^i+^j+3^k) m to →r2=(8t2^i+9t3^j+7t^k) m. Find the instantaneous power delivered by the force at t=1 sec.

- 100 W
- 60 W
- 80 W
- 120 W

**Q.**

How do you define power in terms of energy?

**Q.**

If the heart works 60 joules in one minute. What is its power?