Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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 $10:m/s$:

  1. Equal

  2. 4 times

  3. 2 times

  4. 3 times
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $\displaystyle 10:m/s$  $E _{2}=\frac{1}{2}m(100-0)$

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

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

The number of joules contained in 1kWh is_____

  1. $36 \times 10^2$
  2. $36 \times 10^3$
  3. $36 \times 10^4$
  4. $3.6 \times 10^6$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $3.6\times10^6$.

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

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

  1. kinetic energy

  2. work done

  3. potential energy

  4. all the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. $4.2 Joule$
  2. $0.42 \times {10}^{6} Joule$
  3. $4.2 \times {10}^{6} Joule$
  4. $4.2 \times {10}^{7} Joule$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $1 cal=4.2 J$)

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

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? 

  1. $8\mu W$
  2. $10\mu W$
  3. $4\mu W$
  4. $2\mu W$
Reveal answer Fill a bubble to check yourself
D Correct answer
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