Tag: work, energy and power

Questions Related to work, energy and power

Which of the following statements is true for collisions-

modelling collisions collisions momentum work, energy and power physics

  1. Momentum is conserved in elastic collisions but not in inelastic collisions

  2. Total kinetic energy is conserved in elastic collisions but momentum is not conserved

  3. Total kinetic energy is not conserved in inelastic collisions but momentum is conserved

  4. Total kinetic energy and momentum both are conserved in all types of collisions

Show answer
Correct Option: C
Explanation:

Total momentum and total energy of a system always remain conserved.

In inelastic collisions, some of the kinetic energy goes into the heat energy, with total energy and momentum still being conserved.

For inelastic collision between two spherical rigid bodies: 

modelling collisions collisions momentum work, energy and power physics

  1. The total kinetic energy is conserved

  2. The total potential energy is conserved

  3. The linear momentum is not conserved

  4. The linear momentum is conserved

Show answer
Correct Option: D
Explanation:

In any type of collision, linear momentum is conserved, unless external force acts on the system. elasticity determines the loss in KE. elastic => no loss. inelastic => max. loss of KE ($KE _i - KE _{COM}$)

During a pool game the cue ball is shot at the red ball. When the cue ball strikes the red ball, the cue ball stops dead, and the red ball moves away at the same velocity the cue ball had before the collision. The type of collision represented in this example is:

modelling collisions collisions momentum work, energy and power physics

  1. An elastic collision

  2. A perfectly inelastic collision

  3. An inelastic collision

  4. All of the above

  5. None of the above

Show answer
Correct Option: A
Explanation:

In an elastic collision there is no loss of kinetic energy. If in the given case , balls are of same masses then their kinetic energies will also be same because their velocities are equal and as said , only one ball is moving before and after collision therefore total kinetic energy is constant i.e. it is an elastic collision.

    total kinetic energy before collision= total kinetic energy after collision
                                    $1/2mv^{2}+0=0+1/2mv^{2}$

Identify which of the following quantities remain conserved during an elastic collision?

modelling collisions collisions momentum work, energy and power physics

  1. momentum only

  2. momentum and potential energy

  3. kinetic energy only

  4. momentum and kinetic energy

  5. momentum end velocity

Show answer
Correct Option: D
Explanation:

During collision, net external force acting on the colliding bodies is zero, thus total momentum of the system is conserved in all types of collision.

But total kinetic energy of the system is conserved only in case of elastic collision.
Hence option D is correct.

A bullet is fired into a wooden block. If the bullet gets embedded in wooden block, then:

modelling collisions collisions momentum work, energy and power physics

  1. momentum alone is conserved

  2. kinetic energy alone is conserved

  3. both momentum and kinetic energy are conserved

  4. neither momentum nor kinetic energy are conserved

Show answer
Correct Option: A
Explanation:

The case is of an inelastic collision. In such collisions, energy(kinetic energy) is lost and is therefore not conserved. But, the momentum of the system is conserved in every collision .

During one dimensional collision or head on collision :

a) The bodies move along the line joining their centre of mass before and after collision.
b) The bodies should move in opposite direction.
c) The bodies change their direction after collision.
d) The bodies move along the line joining their centre of mass before and after collision either in same direction or in opposite direction.

modelling collisions collisions momentum work, energy and power physics

  1. Only a is correct

  2. Only a & b are correct

  3. a, b & c are correct

  4. Only a and d are correct

Show answer
Correct Option: D
Explanation:

By the definition of head on collision, the two bodies have to move along the line joining their centers and their velocities can be in any directions (only two possible here).

 Assertion (A) : A body of "$m _{1}$" collides another body of mass "$m _{2}$" at rest elastically. The fraction of energy transferred to the second body is$\dfrac{m _{1}}{m _1+m _{2}}$
Reason (R) : In an "inelastic collision" only linear momentum is conserved

modelling collisions collisions momentum work, energy and power physics

  1. Both Assertion (A) and Reason (R) are correct

    and R is the correct explanation

  2. Both Assertion (A) and Reason (R) are correct but

    the reason does not give the correct explanation

  3. A is true but R is false

  4. A is false but R is true

Show answer
Correct Option: D
Explanation:

In elastic collision no energy loss takes place that is total energy is transferred.
However, in inelastic collision, energy loss takes place and only linear momentum is conserved.

The graph between applied force and change in the length of wire within elastic limit is a ___________.

modelling collisions collisions momentum work, energy and power physics

  1. Straight line with positive slope

  2. Straight line with negative slope

  3. Curve with positive slope

  4. Curve with negative slope

Show answer
Correct Option: A
Explanation:

According to the Hooke's law,

$Y=\dfrac{Stress}{Strain}=\dfrac{F/A}{\Delta x/l}$
$\implies F=\dfrac{YA\Delta x}{l}$
$\implies F\propto \Delta x$
Hence correct answer is option A.

During inelastic collision between two bodies, which of the following quantities always remain conserved?

modelling collisions collisions momentum work, energy and power physics

  1. Total kinetic energy.

  2. Total mechanical energy.

  3. Total linear momentum.

  4. Speed of each body

Show answer
Correct Option: C
Explanation:

Since no external forces are acting on the colliding bodies during collision, thus total linear momentum is always conserved in all type of collisions but kinetic energy in not conserved in all collisions.

Kinetic energy is conserved in perfectly elastic collision only but some kinetic energy is lost in inelastic collisions. So, total kinetic energy is not conserved in inelastic collision.

In an inelastic collision, the kinetic energy after collision

modelling collisions collisions momentum work, energy and power physics

  1. is same as before collision

  2. is always less than that before collision

  3. is always greater than that before collision

  4. may be less or greater than that before collision

Show answer
Correct Option: B
Explanation:

In inelastic collisions , the kinetic energy is used for deforming the the bodies . In such collisions , the reformation of the bodies is partial. Therefore, the potential energy stored in the deformation is lost as heat and the kinetic energy of the system after collision is less than that of before collisions. However, in some cases it may be greater ( such collisions are called super elastic collisions).