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Standard VII
Physics
Law of Conservation of Energy
Question

Before a rubber ball bounces off from the floor, the ball is in contact with the floor for a fraction of second. Which of the following statements are correct?
  1. Conservation of energy is not valid during this period
  2. Conservation of energy is valid during this period
  3. Only the potential energy is conserved
  4. Only the kinetic energy is conserved

A
Conservation of energy is not valid during this period
B
Conservation of energy is valid during this period
C
Only the kinetic energy is conserved
D
Only the potential energy is conserved
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Solution
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The total energy of the ball=Kinetic Energy+Potential Energy
The kinetic energy or the potential energy changes as the ball falls down and hits the floor. But the total energy is always conserved.

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Similar Questions
Q1
Before a rubber ball bounces off from the floor, the ball is in contact with the floor for a fraction of second. Which of the following statements are correct?
View Solution
Q2

Answer carefully, with reasons:

(a) In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact)?

(b) Is the total linear momentum conserved during the short time of an elastic collision of two balls?

(c) What are the answers to (a) and (b) for an inelastic collision?

(d) If the potential energy of two billiard balls depends only on the separation distance between their centres, is the collision elastic or inelastic? (Note, we are talking here of potential energy corresponding to the force during collision, not gravitational potential energy).

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Q3
Assertion: In an elastic collision of two billiard balls, the total kinetic energy is conserved during the short time of oscillation of the balls (i.e., when they are in contact).
Reason: Energy spent against friction does not follow the law of conservation of energy.
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Q4
Answer carefully, with reasons :
(a) In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact) ?
(b) Is the total linear momentum conserved during the short time of an elastic collision of two balls ?

(c) What are the answers to (a) and (b) for an inelastic collision?

(d) If the potential energy of two billiard balls depends only on the separation distance between their centres, is the collision elastic or inelastic? (Note, we are talking here of potential energy corresponding to the force during collision, not gravitational potential energy).

View Solution
Q5

A ball falls to the ground as shown below :

(a) What is the kinetic energy of ball when it hits the ground ?

(b) What is the potential energy of ball at B ?

(c) Which law you have made use of in answering this question ?

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