Tag: different forms of energy

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Questions Related to different forms of energy

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because

  1. its temperature increases

  2. larger amount of potential energy is converted into kinetic energy

  3. the electricity content of water increases with height

  4. more water molecules dissociate into ions
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hydroelectric power plant uses the potential energy stored in water to generate electricity.
Therefore, if we increase the height of it's fall, energy stored will also increase and large amount of potential energy will be converted into kinetic energy, which means more electric energy will be generated.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

Choose the incorrect statement regarding wind power.

  1. Energy from moving wind is wind energy.

  2. The potential energy content of wind blowing at high altitudes is the source of wind power.

  3. Wind hitting at the blades of a windmill causes them to rotate. The rotation thus achieved can be utilized further.

  4. One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The energy that we harness from a windmill is the wind energy due to moving air.
Here, option B is wrong as the wind energy does not depend on the altitude when we harness energy from the windmill.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

Water falls from a height 500 m. What is the rise in  temperature of water at bottom if whole energy remains in the water?

  1. $0.96^0C$
  2. $1.02^oC$
  3. $1.17^oC$
  4. $0.23^oC$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Water is at height $(h) = 500 \,m$.
Potential energy $= mgh$
$= 1 \times 9.81 \times 500$
$= 4905 \,J/litre$

Specific heat of water $= 4180 \,J/kg \,k$.
So, $E = mc \Delta T$.
$4905 = 1 \times 4180 \times \Delta T$
$\Delta T = \dfrac{4905}{4180}$
$\Delta T = 1.16^o C$.
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

When we rub our hands, which of the following is true?

  1. Mechanical energy converted to heat energy.

  2. kinetic energy converted to heat energy.

  3. Heat energy converted to mechanical energy.

  4. Heat energy converted to kinetic energy.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rubbing hands involves the movement of muscles (mechanical energy), and the friction generated converts that motion into heat energy.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A body off mass $5kg$ falls from a height of $30metre$. If its all mechanical energy is changed into heat, then heat produced will be 

  1. $ \text{350 cal} $
  2. $ \text{150 cal} $
  3. $ \text{60 cal} $
  4. $ \text{6 cal} $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Potential energy = mgh = 5 * 9.8 * 30 = 1470 Joules. Since 1 calorie is approximately 4.2 Joules, 1470 / 4.2 = 350 calories.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

a piece of lead falls from a height of $100m$ on a fixed non-conducting slab which brings it to rest. If the specific heat of lead is $30.6{\rm{ }}cal/kg{\,^ \circ }C,$, the increase in temperature of the slab immediately after collision is 

  1. ${6.72^ \circ }C$
  2. ${7.62^ \circ }C$
  3. ${5.62^ \circ }C$
  4. ${8.72^ \circ }C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The potential energy lost by the falling lead piece is converted entirely into heat energy in the slab and lead, assuming no heat loss. Using mgh = m * s * Delta T, where m cancels out, we find Delta T = (g * h) / s. Substituting g = 9.8 or 9.81, h = 100m, and specific heat s = 30.6 cal/kg C (converted to joules if needed, or using direct units where 1 cal = 4.184 J), the temperature increase calculates to approximately 7.62 degrees Celsius.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

The temperature inside and outside a refrigerator are $273\ K$ and $300\ K$ respectively Assuming that the refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be nearly

  1. $11\ J$
  2. $22\ J$
  3. $33\ J$
  4. $50\ J$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For a reversible refrigerator, the coefficient of performance is COP = T_L / (T_H - T_L) = 273 / (300 - 273) = 273 / 27. The heat delivered to the surroundings is Q_H = W + Q_L. Since COP = Q_L / W, Q_L = COP * W = (273 / 27) * 1 = 273 / 27 J. Then Q_H = W + Q_L = 1 + 273 / 27 = 300 / 27 = 11.11 J, which is nearly 11 J.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

The height of the Niagara falls is $50$ metres, $(1 cal= 4.2 \mathrm\ { J }).$  Assume its mechanical energy can be completely converted into heat energy.

  1. Heat energy gained by each gram of water is $49 \times 10 ^ { 5 }\ \mathrm { cal }$
  2. Rise in temperature of water is $0.166^{ o }\ C/g$
  3. Rise in temperature of water is $0.12^{ o }\ C$
  4. Heal energy gained is $500\ joule/g$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

The units of fore and length are made three times of their earlier values. Earlier the energy of a system was $81\ J$. What will be the energy of the same system in new units?

  1. $243$
  2. $729$
  3. $9$
  4. $None\ of\ the\ above$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Energy has dimensions [M L^2 T^-2]. If force [M L T^-2] and length [L] are tripled, then [M L T^-2] -> 3 and [L] -> 3. This implies [M] -> 3 / 3 = 1 and [T^-2] -> 3 / 3 = 1 (no change). Thus, energy scales by [M] * [L]^2 * [T^-2] = 1 * 3^2 * 1 = 9. New energy = 81 * 9 = 729 J.