Tag: physics

Questions Related to physics

A machine gun is mounted on a 2000 kg car on a horizontal frictionless surface. At some instant, the gun fires 10 bullets/second, each of mass 10 g with a velocity of 500 m s$^{-1}$. The acceleration of the car is

physics lever common machines terms related to machines introduction to simple machines

  1. 0.025 ms$^{-2}$

  2. 0.25 ms$^{-2}$

  3. 0.5 ms$^{-2}$

  4. 500 ms$^{-2}$

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Correct Option: A
Explanation:

$M _{car}=2000kg$


$n=10 \ bullets/s$

$M _{b}=10g=0.01kg$

$V _{b}=500m/s$

Momentum of each bullet $=0.01\times 500$

$(M _{b}V _{b})P _{b}=5kgm/s$

Force on car $=nP _{b}$

                       $50kgm/s^{2}$
$F _{car}=50N$

$a _{car}=\dfrac{50}{2000}=\dfrac{1}{40}$

$a _{car}=0.025m/s^{2}$

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?

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

  1. $Chemical \rightarrow gravitational\ potential\rightarrow kinetic$

  2. $Chemical \rightarrow kinetic \rightarrow gravitational\ potential$

  3. $Gravitational\ potential \rightarrow chemical \rightarrow kinetic$

  4. $Kinetic \rightarrow chemical \rightarrow gravitational\ potential$

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Correct Option: B
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.

The plants trap solar energy in the form of :

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

  1. physical energy

  2. chemical energy

  3. heat energy

  4. light energy

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Correct Option: B
Explanation:

When sunlight falls on plant, some of the energy is trapped through
photosynthesis and is stored in the form of chemical energy which helps the plants to prepare their own food.

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

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

  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.

Show answer
Correct Option: D
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.

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

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

  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

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Correct Option: A
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.

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

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

  1. Potential energy

  2. Kinetic energy

  3. Heat energy

  4. None of the above

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Correct Option: B
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.

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

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

  1. magnetic energy

  2. light energy

  3. kinetic energy

  4. heat energy

Show answer
Correct Option: C
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.

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.

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

  1. heat; light

  2. light; heat

  3. mechanical; heat

  4. mechanical; light

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Correct Option: A
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.

A metal ball of mass $2kg$ is allowed to fall freely from rest from a height of $5m$ above the ground (Take $g=10ms^{-2}$). After the ball hits the ground and comes to rest, mechanical energy is converted to:

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

  1. heat energy

  2. sound energy

  3. electrical energy

  4. Both A & B

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Correct Option: D
Explanation:

When ball is at rest it will have only P.E that is
$P.E = mgh$


$m = 2\  kg; h = 5\  m$

$P.E = 2\times 10\times 5 = 100 J$

This is the total energy as K.E is zero when ball is at maximum height that is when it is at 5m. Hence when ball reaches the ground P.E becomes zero  because height is zero. At this point total energy is equal to K.E that is $K.E = 100 J$.

This $100\  J$ will convert to heat and sound energy as the ball comes to rest.

State whether the given statement is True or False :

A freely falling object eventually stops on reaching the ground. A part of the kinetic energy on reaching the ground changes into heat energy.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The kinetic energy on reaching the ground changes into heat energy, sound energy, etc. and therefore gets dissipated to the ground and air.