std 9 science ch 2 work and energy question answer |Exercise std 9 sci ch 2 question answer
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Exercise class 9 science chapter 2 work and energy,
Question answer, Workshop, Std 9 science, Exercise
work and energy, Class 9 science chapter 2, Class 9
science work and energy, Question answer work and
energy, Std 9 science work and energy, Class 9
science work and energy,
. Write detailed answers?
Exercises
a. Explain the difference between
potential energy and kinetic energy.
b. Derive the formula for the kinetic
energy of an object of mass m,
moving with velocity v.
c. Prove that the kinetic energy of a
freely falling object on reaching
the ground is nothing but the
transformation of its initial potential
energy.
d. Determine the amount of work
done when an object is displaced at
an angle of 30° with respect to the
direction of the applied force.
e. If an object has 0 momentum, does
it have kinetic energy? Explain your
answer.
f. Why is the work done on an object
moving with uniform circular
motion zero?
2. Choose one or more correct alterna-
tives.
28
e. While dragging or lifting an object,
negative work is done by
(i) the applied force (ii) gravitational
force (iii) frictional force
(iv) reaction force
3. Rewrite the following sentences
using proper alternative.
a. The potential energy of your body is
least when you are .....
(i) sitting on a chair (ii) sitting on
the ground (iii) sleeping on the
ground (iv) standing on the ground
b. The total energy of an object falling
freely towards the ground ...
(i) decreases (ii) remains unchanged
(iii) increases (iv) increases in the
beginning and then decreases
c. If we increase the velocity of a car
moving on a flat surface to four
times its original speed, its potential
a. For work to be performed, energy
must be ....
(i) transferred from one place to
another (ii) concentrated.
(iii) transformed from one type to
another (iv) destroyed
b. Joule is the unit of ....
(i) force (ii) work (iii) power
(iv) energy
c. Which of the forces involved in
dragging a heavy object on a
smooth, horizontal surface, have
the same magnitude?
(i) the horizontal applied force (ii)
gravitational force (iii) reaction
force in vertical direction (iv) force
of friction
d. Power is a measure of the .......
(i) the rapidity with which work is
done (ii) amount of energy required
to perform the work (iii) The
slowness with which work is
performed (iv) length of time
Questions
1. At the moment of releasing the
balls, which energy do the balls
have?
2. As the balls roll down which energy
is converted into which other form
of energy?
3. Why do the balls cover the same
distance on rolling down?
4. What is the form of the eventual
total energy of the balls?
5. Which law related to energy does
the above activity demonstrate ?
Explain.
5. Solve the following examples.
a. An electric pump has 2 kW power.
How much water will the pump lift
every minute to a height of 10 m?
(Ans: 1224.5 kg)
.
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