Power

Q. the dimensions of time in energy ar

Q.

A car of mass 1250 kg experience a resistance of 750 N when it moves at $30m{s}^{-1}$. If the engine can develop 30kW at this speed, the maximum acceleration that the engine can produce is

1. 

2. 

3. 

4. 

Q. find work done by object moving upward on a inclined plane. Explain it fully detail with reson of every thing.

Q. At temperature T, the power related by a body Q watts. At the temperature 2T the power radiated by it will be

Q.

A man $M_1$ of mass 80 kg runs up a staircase in 15 s. Another man M₂ also of mass 80 kg runs up the same staircase in 20 s. The ratio of the powers developed by them will be

1. 

2. 

3. None of these

4. 1

Q.

A man is riding on a cycle with velocity 7.2 km/hr up a hill having a slope 1 in 20. The total mass of the man and cycle is 100 kg. The power of the man is

1. 125 W

2. 98 W

3. 200 W

4. 175 W

Q. Hydroelectric power station takes its water from a lake whose level is at height of 50 metre above the turbine. Assuming and overall efficiency of 40%, calculate the mass of water which must flow through the turbine each second to produce power output of 1MW. ( Take g = 10m/s2 )

Q.

An astronomer has total weight of 80 kg. On reaching moon, he climbs up 10 m to enter his aircraft by the ladder. His gravitational potential energy is increased by 1000 J. The value of the gravitational acceleration on the moon is

1. 2.22 kg

2. 1.25 N/kg

3. 2 N/kg

4. 2.25 kg

Q.

A force of 100 dynes acts on mass of 5 gm for 10 sec. The velocity produced is

1. 2 cm/sec

2. 2 cm/sec

3. 200 cm/sec

4. 2000 cm/sec

Q.

A 100 kg block is started with a speed of $2.0m{s}^{-1}$ on a long, rough belt kept fixed in a horizontal position. The coefficient of kinetic friction between the block and the belt is 0.20.

If the same experiment is carried out in vacuum inside an adiabatic chamber, the change in internal energy of the belt-block system will be -

1. 200 J

2. 0 J

3. 100 J

4. 400 J

Q. A (3i + 4j) N force acting on a body displaces it by (3i + 4j) m. The work done by the force is

1. 25 J
2. 7 J
3. 5 J
4. zero

Q. 112.A spherical black body with radius 12 cm radiates 450 W power at 500 K.If the radius is halved and temperature is doubled, the power radiated in watt would be.

Q. power unit is 1kwatt length 100m time is 1s what will be the unit of mass

Q. A charge $2\mu \text{C}$ is taken from infinity to any point $P\text{(say)}$ in an electric field, without changing its velocity. If workdone against electrostatic forces is $-40\mu \text{J}$, then the electric potential at that point will be:

1. $+10\text{V}$
2. $-20\text{V}$
3. $+20\text{V}$
4. $-10\text{V}$

Q. The blades of a windmill sweep out a circle of area A.
(a) If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t?
(b) What is the kinetic energy of the air?
(c) Assume that the windmill converts 25% of the winds energy into electrical energy, and that A = 30 $m^2$, v = 36 km/h and the density of air is 1.2 kg $m^3$. What is the electrical power produced?

Q. In a new system of units energy, density, and power are taken as fundamental units, then the dimensional formula of universally gravitionalconstant "G" will be?

Q. A 120 volt A.C line provides power to 48 Watt bulb (rated at 120v). If a capacitor of capacitance $2.5\mu F$ is connected in series with the bulb, then the output power of the bulb is $[\omega ={10}^{3}rad/s]$

1. 20 Watt
2. 17.28 Watt
3. 13.3 Watt
4. 35.7 Watt

Q. A neutral pendulum oscillates in a uniform electric field as shown in figure. If a positive charge is given to the pendulum, then its time period
Assume that $mg>qE$

1. will first increase then decrease.
2. will increase.
3. will remain constant.
4. will decrease.

Q.
$i=15\sin \omega t+20\cos \omega t$.
Alternating current $i$ is passed through a resistance of $8\Omega$. Find the heat developed across R in 10 seconds.

1. $25\times {10}^3$ J
2. $125\times {10}^2$ J
3. $625\times {10}^2$ J
4. $5\times {10}^4$ J

Q. In the given RLC circuit power dissipation if frequency is half of resonant frequency

1. 80 watt
2. 50 watt
3. 40 watt
4. 20 watt

Q. A torch bulb rated as $4.5W-1.5V$ is connected as shown in the figure. The emf of the cell needed to make the bulb glow at full intensity is

1. $4.5V$
2. $1.5V$
3. $2.67V$
4. $13.5V$

Q. A water pump lifts water from 10 m below the ground. Water is pumped at a rate of 30 kg/minute with negligible velocity. Calculate the minimum horsepower that the engine should have to do this.

Q. A battery is charged at a potential of $15V$ for $8h$ when the current flowing is $10A$. The battery on discharge supplies a current of $5A$ for $15h$. The mean terminal voltage during discharge is $14V$. The watt-hour efficiency of the battery is

1. $82.5\%$
2. $80\%$
3. $90\%$
4. $87.5\%$

Q. How to learn prefix for power of ten

Q. From a dam water is pouringdown at the rate of 150kg/s on the blades of a turbine if a ball dropped from the same dam takes 2 \sqrt5 s to hit the turbine then the power delivered to the turbine is approximately equal to (a)15W (b)150kW (c)125 kW (d)15.5 k

Q. If a motor pumps 10kilogram water in 1minut from the depth of 600metre. If the process goes on for 1 hour .Find the work done by the engine and also find the height of a ball of 250gram if it would be projected by the same amount of energy.

Q. In a factory, 2000 kg of metal needs to be lifted by an engine through a distance of 12 m in 1 minute. Find the minimum horsepower of the engine to be used.

Q. What is the work done by the gravity on the moon revolving around the earth ? Justify.

Q. Hydroelectric power station takes its water from a lake whose level is at height of 50 metre above the turbine. Assuming and overall efficiency of 40%, calculate the mass of water which must flow through the turbine each second to produce power output of 1MW. ( Take g = 10m/s2 )

Q.

Q1=The turbine pits at the NIagra falls are 50 m deep .The average h.p developed is 5000, the efficiency is 85%.How much water passes through the turbines per minute?use g=10m/s² .