Tag: energy and its forms

Questions Related to energy and its forms

The energy required to accelerate a car from $10:m/s$ to $20:m/s$ is how many times the energy required to accelerate the car from the rest to $10:m/s$:

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

  1. Equal

  2. 4 times

  3. 2 times

  4. 3 times

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Correct Option: D
Explanation:

Energy required to accelerate from $\displaystyle 10:m/s$ to $20:m/s$ $E _{1}=\frac{1}{2}m(400-100)$


Energy  required to accelerate from rest to $\displaystyle 10:m/s$  $E _{2}=\frac{1}{2}m(100-0)$

$\displaystyle \frac{E _{1}}{E _{2}}=\frac{\frac{1}{2}m(300)}{\frac{1}{2}m(100)}=3:times$

Cost of electricity for home use is Rs. 1.50 per unit. This unit is:

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

  1. 1 ampere

  2. 1 volt

  3. 1 joule

  4. 1 kilowatt hour

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Correct Option: D
Explanation:

The electrical unit for the electricity of home is used as kilowatt hour (kWh). Here the cost of 1 kWh electricity is Rs 150.  

The unit $kg m^2s^{-2}$ is associated with:

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

  1. work

  2. kinetic energy

  3. potential energy

  4. all the above

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Correct Option: D
Explanation:

This is unit of energy $ML^2T^{-2}$ (in dimensional form).

All the quantities given in the option are different form of energy ao their units will be same. So the given unit is associated with all.

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. $3.6 \times 10^6$

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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

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

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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. $3.6MJ$

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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

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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. $3.6GJ$

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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