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CBSE Questions for Class 9 Physics Work And Energy Quiz 16 - MCQExams.com
CBSE
Class 9 Physics
Work And Energy
Quiz 16
At the start of the free-fall of an object from height $$h$$, the potential energy is _____ and kinetic energy is _____.
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Zero, $$mgh$$
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$$mgh$$, infinite
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Infinite, $$mgh$$
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$$mgh$$, zero
Explanation
Given,
At the start of the free-fall of an object from height $$h$$
Initial velocity, $$v=0$$ (at rest)
Acceleration due to gravity, $$g$$
Let the mass of the object be $$m$$
Potential energy, $$U=mgh$$
Kinetic energy, $$KE=\dfrac 12mv^2$$
$$KE=\dfrac 12m(0)^2$$
$$KE=0$$
Bullet $$2$$ has twice the mass of bullet $$1$$. Both are fired so that they have the same speed. If the kinetic energy of bullet $$1$$ is $$K$$, is the kinetic energy of bullet $$2$$
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$$0.25K$$
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$$0.5K$$
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$$0.71K$$
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$$K$$
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$$2K$$
Explanation
Let $$m$$ be the mass of bullet $$1$$.
According to the given condition, the mass of bullet $$2$$ is $$2m.$$
Kinetic energy of bullet $$1$$ is
$$KE_1=\dfrac{1}{2}mv^2=K$$
KE of bullet $$2$$ is
$$KE_2=\dfrac{1}{2}(2m)v^2=2(\dfrac{1}{2}mv^2)=2K$$
We can explain free-fall of an object on the basis of?
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Work-energy theorem
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Conservation of Kinetic energy
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Conservation of potential energy
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Conservation of energy
Explanation
According to the law of conservation of energy, energy can only be converted from one form to another; it can neither be created or destroyed. The total energy before and after the transformation remains the same. The law of conservation of energy is valid in all situations and for all kinds of transformations for example, the free-fall of an object.
When a body starts falling, it posses only potential energy. As it falls, its potential energy decreases and converts into kinetic energy . Finally, at the lowest point, it has only kinetic energy. So, during free fall, the body converts potential energy into kinetic energy.But the sum of $$KE$$ and $$PE$$ at any instant during the fall will be same .Hence total energy is conserved.
Choose whether true or false:-
Kinetic enegry can be written in the form of an equation.
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True
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False
Explanation
The kinetic energy possessed by an
object of mass $$m$$, and moving with a uniform
velocity $$v$$ is,
$$E_K$$ = 1/2$$m$$$$v^2$$. Hence the given statement is true.
Whenever energy gets transformed, the total energy_______.
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Varies with time
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Varies with position
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Remains unchanged
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None of these
As the fall of the object continues, the potential energy would ________ while the kinetic energy would ______.
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decrease, decrease
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increase, decrease
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decrease, increase
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increase, increase
Explanation
As the fall of the object continues, the potential energy would decrease while the kinetic energy would increase, hence option $$C$$ is correct.
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