Power

Q.

Differentiate between power and energy.

Q.

The speed of work being done is measured in terms of:

1. change in momentum

2. impulse

3. intensity of work

4. power

Q. Question 26
How is the power related to the speed at which a body can be lifted? How many kilograms will a man working at the power of 100 W, be able to lift at constant speed of $1m{s}^{-1}$ vertically? $(g=10m{s}^{-2})$

Q. One watt-hour is equivalent to :

1. $3.6\times {10}^3$ Joule
2. $3.6\times {10}^{-3}$ Joule
3. $6.3\times {10}^{-3}$ Joule
4. $6.3\times {10}^3$ Joule

Q. $1kW$ is equal to :

1. $1000watt$
2. ${10}^{-3}megawatt$
3. $A$ and $B$ both
4. neither $A$ nor $B$

Q.

An electric fan consumes 1500 J of energy in half an minute. The power of fan is _____ ?

1. 50 Watt

2. 150$J{s}^{-1}$

3. 45 Watt

4. 200 $J{s}^{-1}$

Q. An electric heater of power $3kW$ is used for $10h$. How much energy does it consume? Express you answer in $kWh$.

1. $0.3kWh$
2. $3kWh$
3. $30kWh$
4. $30Wh$

Q.

Define 1 Watt.

Q. Watt-hour measures

1. current
2. power
3. voltage
4. electric energy

Q. Assertion :The kinetic energy, with any reference, must be positive. Reason: In the expression for kinetic energy, the velocity appears with power 2.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Assertion is incorrect but Reason is correct

Q.

A particle of mass 1 kg was sliding with a velocity of 10 m/s on a rough floor. It comes to rest after 5 s. The rate at which floor warms up is

___ W.

Q.

Two cars A and B with a mass of 5 kg and 10 kg and initial velocities of $10m{s}^{-1}$ and $5m{s}^{-1}$ are racing. Which car exerts more power before coming to rest? (Time taken for both cars to complete the race is 10 seconds):

1. Data insufficient

2. B

3. Both exert same power

4. A

Q. If power is increased by $50\%$ and work done is constant, then the time taken is reduced by:

1. $50\%$
2. $0\%$
3. $66.66\%$
4. $33.33\%$

Q.

A 60 kg skydiver moving at terminal speed 40 m in 2 seconds. The sky diver is spending a power of

___ KW.

Q. From a waterfall, water pours down at the rate of $100kg{s}^{-1}$ on the blades of a turbine. If the height of the fall is 120 m, what is the power delivered to the turbine?

1. 120 kW
2. 120 W
3. 125 kW
4. 1.2 W

Q. In a tug of war match, team A displaces team B by 30 cm from the reference line. The forces applied by team A and B are 150 N and 120 N respectively. Calculate the energy spent by team A.

1. 400 J
2. 45 J
3. 500 J
4. 36 J

Q.

An electric heater is rated $1500W$. The energy used by it in $10hours$ is:

1. $5kWh$

2. $10kWh$

3. $15kWh$

4. $20kWh$

Q. The commercial unit of power is kWh, which is equal to:

1. $1.3\times$ ${10}^5\text{joules}$
2. $3.6\times$ ${10}^6\text{joules}$​
3. $3.6\times$ ${10}^5\text{joules}$​
4. $1.3\times$ ${10}^6\text{joules}$​

Q. The value of the resistance $R$ in the circuit shown so that electric bulb consumes the rated power is:

1. $4$ ohm
2. $6$ ohm
3. $8$ ohm
4. $10$ ohm

Q.

A 60 kg skydiver moving at terminal speed 40 m in 2 seconds. The sky diver is spending a power of

___ KW.

Q. What is the heating effect of electric current? Give a few real-life examples where it is used. 3 Marks

Q. An automobile has a mass of 1 500 kg, and its aluminum brakes have an overall mass of 6.00 kg. (a) Assume all the mechanical energy that transforms into internal energy when the car stops is deposited in the brakes and no energy is transferred out of the brakes by heat.The brakes are originally at ${20.0}^{0}C$. How many times can the car be stopped from 25.0 m/s before the brakes start to melt? (b) Identify some effects ignored in part(a) that are important in a more realistic assessment of the warming of the brakes.