Tag: energy transformations and energy transfers

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Questions Related to energy transformations and energy transfers

Multiple choice physics energy transformations and energy transfers forms of energy and energy conservation energy for everything forms of energy

A charged parallel plate capacitor of distance ($d$) has ${U} _{0}$ energy. A slab of dielectric constant ($K$) and thickness ($d$) is then introduced between the plates of the capacitor. The new energy of the system is given by:

  1. $K{U} _{0}$
  2. ${K}^{2}{U} _{0}$
  3. $\cfrac{{U} _{0}}{K}$
  4. $\cfrac{{U} _{0}}{{K}^{2}}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When a dielectric slab of constant K completely fills the space between the plates of a charged disconnected capacitor, the capacitance increases by a factor of K, becoming C equals K times C0. Since the charge remains constant, the stored energy U equals Q squared divided by 2C, which means the new energy becomes the initial energy divided by K.

Multiple choice physics energy transformations and energy transfers forms of energy and energy conservation energy for everything forms of energy

 person trying to lose weight by burning fat lifts a mass of $10kg$ upto a height of $0.5\, m\, with\, in\, 1000$ times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up? Fat supplies $3.8 \times 10^7 J$ of energy per kg which is converted to mechanical energy with a $20 \%$ efficiency rate. 

  1. $6.45 \times {10^{ - 3}}kg$
  2. $9.89 \times {10^{ - 3}}kg$
  3. $12.89 \times {10^{ - 3}}kg$
  4. $2.45 \times {10^{ - 3}}kg$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Work done per lift = mgh = 10 * 9.8 * 0.5 = 49 J. Total work for 1000 lifts = 49,000 J. With 20% efficiency, energy required from fat = 49,000 / 0.20 = 245,000 J. Fat energy density = 3.8 * 10^7 J/kg. Mass of fat = 245,000 / (3.8 * 10^7) = 6.447 * 10^-3 kg.

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

A helicopter takes off from the ground and rises vertically. It then hovers at a constant height
above the ground.
Which sequence of energy changes takes place during the gain in height?

  1. $Chemical \rightarrow gravitational\ potential\rightarrow kinetic$
  2. $Chemical \rightarrow kinetic \rightarrow gravitational\ potential$
  3. $Gravitational\ potential \rightarrow chemical \rightarrow kinetic$
  4. $Kinetic \rightarrow chemical \rightarrow gravitational\ potential$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

First the fuel in the engine gives chemical energy during burning. That chemical energy then converts to kinetic energy if the rotor of blades of the helicopter. Then kinetic energy converts in gravitational potential energy as it gains height.

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

Identify the energy changes in the following cases
$A$: A car moving up a hill.
$B$: Photographic film is exposed to sun-light.

  1. In $'A'$ mechanical energy in moving car is converted to kinetic energy and in $'B'$ potential energy is converted to chemical energy.
  2. In $'A'$ potential energy in moving car is converted to kinetic energy and in $'B'$ chemical energy is converted to light energy.
  3. In $'A'$ kinetic energy in moving car is converted to potential energy and in $'B'$ potential energy is converted to light energy.
  4. In $'A'$ kinetic energy in moving car is converted to potential energy and in $'B'$ light energy is converted to chemical energy.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$A$: A car moving up a hill.
Moving car has kinetic energy, kinetic energy gets converted to potential energy as it gains height $(h)$.
And potential energy $=mgh$
$B$: Photographic film is exposed to sun -light.
When photographic film is exposed to Sun the silver bromide present in it decomposes, such that the film cannot be developed, here the light energy changes to chemical energy.

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

What are the various energy transformations that occur when you are riding a bicycle ?

  1. Muscular energy to kinetic and heat energy

  2. Mechanical energy to chemical and light energy

  3. Chemical energy to Internal energy

  4. Rotational energy to muscular energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

While riding a bicycle,the muscular energy of the rider gets transferred to heat energy and kinetic energy of the bicycle.Heat energy heats the rider's body.Kinetic energy provides a velocity to the bicycle to move in rotation.The transformation can be shown as:
Muscular energy$=$kinetic energy+heat energy
During transformation,the total energy remains conserved.

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

A ball falls freely under gravity from rest. Name the kind of energy it will possess on reaching the ground.

  1. Potential energy

  2. Kinetic energy

  3. Heat energy

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

After reaching the ground it will not have any height from the ground hence no potential energy as it is defined as virtue of state of its position where as it has velocity by which it can be said that kinetic energy exists as it is defined by virtue of state of its motion.While falling potential energy keeps on changing in kinetic energy and on reaching the ground all potential energy changes to kinetic energy.Hence there exists only kinetic energy.

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

As the water stored in the reservoir of a dam flows out, its potential energy changes to :

  1. magnetic energy

  2. light energy

  3. kinetic energy

  4. heat energy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation


The potential energy stored in a reservoir at a given height is converted to kinetic energy (movement energy) which is used to turn a turbine and produce electricity.
Hence, as the water stored in the dam flows out, its potential energy changes to kinetic energy.

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

A battery lights a bulb. The electric energy on flowing through the filament of the bulb, first changes into ______ energy and then into the _______ energy.

  1. heat; light

  2. light; heat

  3. mechanical; heat

  4. mechanical; light
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Within the electric cell or battery, the chemical energy changes into electrical energy. The electric energy on flowing through the filament of the bulb, first changes into heat energy and then into the light energy.