Tag: work and energy

Questions Related to work and energy

The number of joules contained in 1kWh is_____

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $36 \times 10^2$

  2. $36 \times 10^3$

  3. $36 \times 10^4$

  4. $3.6 \times 10^6$

Show answer
Correct Option: D
Explanation:

The kilowatt hour is a unit of energy equal to 3.6 megajoules. If the energy is being transmitted or used at a constant rate over a period of time, the total energy in kilowatt hours is the power in kilowatts multiplied by the time in hours.

Let energy is used as 1J/s. For an hour or 3600 sec. Then total energy used is 3600J. And kWh means 1000$\times$3600.
Which gives $3.6\times10^6$.

$ kg  m^2 s^{-2}$ represents the unit of_____

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. kinetic energy

  2. work done

  3. potential energy

  4. all the above

Show answer
Correct Option: D
Explanation:

the given unit $kgm^2s^{-2}$ is unit of energy and  any of the energy either potential or kinetic will have  same unit 

also work done is given by $F.S$ or $kgms^{-2}.m$ or $kgm^2s^{-2}$
so the unit of work is also same.
so the given unit represent unit for all the three quantities in the options.

Work required to produce $1000   k$ - calorie heat will be

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $4.2 Joule$

  2. $0.42 \times {10}^{6} Joule$

  3. $4.2 \times {10}^{6} Joule$

  4. $4.2 \times {10}^{7} Joule$

Show answer
Correct Option: C
Explanation:

In this problem, we have to convert the heat energy in unit from calorie to Joule. 

According to work-energy theorem, the work is also a energy. 
Thus, $1000k.cal=1000\times 10^3 cal=10^6 cal=4.2\times 10^6 J$  (as $1 cal=4.2 J$)

$1Wh=$

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $36kJ$

  2. $3.6kJ$

  3. $3600kJ$

  4. $3.6MJ$

Show answer
Correct Option: B
Explanation:

$1Wh=1W\times{1h}$

$=1{J}.{s}^{-1}\times{3600}s$

$=3600J=3.6kJ$

Kilowatt-hour is the unit of

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. potential difference

  2. electric power

  3. electrical energy

  4. charge

Show answer
Correct Option: C
Explanation:

Electrical energy $V \times l \times t$
Electric energy unit $= kW  hour$

$1kWh=$

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $3.6J$

  2. $3.6kJ$

  3. $3.6MJ$

  4. $3.6GJ$

Show answer
Correct Option: C
Explanation:

$1kWh=1kW\times{1h}$

$=1000{J}.{s}^{-1}\times{3600}s$

$=3.6\times{10}^{6}J=3.6MJ$

A window whose area is $2m^2$ opens on street where the street noise result in an intensity level at the window of $60db$. How much acoustic power enters the window via sound waves ? Now, if an acoustic absorber is fitted at the window? 

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $8\mu W$

  2. $10\mu W$

  3. $4\mu W$

  4. $2\mu W$

Show answer
Correct Option: D
Explanation:

Intensity = 60 dB

60 = 10 log $(\frac{I}{I _{ref}})$

where $I _{ref}$ is the refrence intensity , general value of this is given by 

$I _{ref} = 10^{-12}\frac{watt}{m^2}$

$\frac{I}{10^{-12}}$ = anti log (6)

$I = 10^{-12}  \times{anti log(6)} = 10^{-12} \times{10^6} = 10^{-6}$

Power = I$\times$ area = $2 \times{10^{-6}}$ watt

The internal energy change when a system goes from state A to B is $40$ kJ/mole. If the system goes from A to B by a reversible path and returns to state A by an irreversible path what would be the net change in internal energy?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $40$ kJ

  2. $> 40$ kJ

  3. $< 40$ kJ

  4. Zero

Show answer
Correct Option: D
Explanation:
For a cyclic process the net change in the internal energy is zero because the change in internal energy doesnot depend on the path.

Which of the following can be negative 

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. Kinetic energy

  2. Potential energy

  3. Mechanical energy

  4. All of these

Show answer
Correct Option: B,C
Explanation:

Mechanical energy & potential energy can be negative.

$\therefore$ Option $B$ and $C$.

If the unit of force and length be each increased by four times, then the unit of energy is increased by

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. 16 times

  2. 8 times

  3. 2 times

  4. 4 times

Show answer
Correct Option: A
Explanation:

Unit of Energy = Unit of Force $\times$ Unit of length 
So if we increase unit of length and force, each by four times, then unit of energy will increase by sixteen times.