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Physics 1 Marks Question

PART - 1 CH - 5Work, Energy and Power · Gujarat Board (GSEB) STD 11 Science (GSEB - English Medium). 40 questions.

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Question 11 Mark
A shell is fired from a cannon and it explodes at the top. What will be the change in its momentum and kinetic energy?
Answer
Momentum will remain constant. Kinetic energy will increase as the chemical energy of the gun powder is converted into kinetic energy.
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Question 21 Mark
The velocity of an airplane is tripled. what will be the momentum? Will momentum be conserved?
Answer
The momentum of the airplane will be tripled. The momentum of the ship + air will be conserved because as the momentum of the ship increases the momentum of the air will increase in the opposite direction.
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Question 31 Mark
Is the complete kinetic energy dissipated in a perfectly elastic collision?
Answer
No, only that much of kinetic energy is last which is necessary for linear momentum conservation.
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Question 41 Mark
Write the name of that parameter of elasticity of an object which is called its measurement degree
Answer
Coefficient of restitution.
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Question 51 Mark
When is the energy exchange maximum in an elastic collision?
Answer
When the two constitutent object are of equal mass.
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Question 61 Mark
Where is the speed of the oscillating pendulum maximum?
Answer
At the minimum point of pendulumAt the minimum point of pendulum.
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Question 71 Mark
When two quarter balls collide with each other, what type of collision occurs?
Answer
Perfectly elastic collision.
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Question 81 Mark
When there is a collision between a negatively charged object and a positively charged object then what type of collision occurs?
Answer
Completely inelastic.
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Question 91 Mark
In a simple linear elastic collision, if a particle collides with a particle of same mass then what is the relationship between the velocities of the particles after the collision?
Answer
After collision, the velocities of the particle interchange with each other
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Question 101 Mark
In a gravitiaonal field, the total mechanical energy of a freely falling object increases. In this statement true or false?
Answer
false
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Question 121 Mark
What is the value of restitution coefficient in a perfectly elastic collision?
Answer
Restitution coefficient e = 1
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Question 141 Mark
The kinetic energy of an object is 40 joules, if its mass is 5 kg then what will be the velocity of the object?
Answer

$\begin{aligned}
K . E . & =\frac{1}{2} m v^2 \\
40 & =\frac{1}{2} \times 5 \times v^2 \\
v^2 & =16 \\
v & =4 m / s
\end{aligned}$
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Question 151 Mark
What should be the minimum number of unequal forces acting on a particle such that the resultant force becomes zero?
Answer
The number of forces acting on any particle should be three whose resultant force will be zero.
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Question 161 Mark
Can an object have energy without momentum?
Answer
Yes, there is intermal energy due to thermal motion of the particles of the object, whereas the vector sum of the momentum of the moving particles can be zero.
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Question 171 Mark
It it possible that work can be done by a force even when there is no motion?
Answer
Yes, by pressing or pulling the spring.
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Question 181 Mark
What is the effect on the value of potential energy if the height of the object is more or increases from earth's surface?
Answer
The value of potential energy will be higher.
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Question 191 Mark
What should be the angle between force and displacement for maximum and minimum work?
Answer
Work, $W = FS \cos \theta$
When the value of angle is zero then the work is maximum. When angle is $90^{\circ}$ then work $W = FS \cos 90^{\circ}$, i.e. work will be zero.
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Question 201 Mark
What is power?
Answer
 Raste of doing work is called power.
$P=\frac{W}{t}=\frac{\text { Work }}{\text { Time }}$
Its unit is Joule/sec.
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Question 211 Mark
Find the number of joules in a kilowatt hour.
Answer

$\begin{array}{l} 1 kWh =1000 \times 1 \text { watt hour } \\ =1000 \times 3600 \\ =36 \times 10^5 J=3.6 \times 10^6 J\end{array}$
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Question 221 Mark
Why the work done by centripetal force on a particle moving in a circular path is zero?
Answer
This force changes only the direction of motion of the particle and the value of speed remains the same and the kinetic energy also remains the same.
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Question 231 Mark
The work done by centripetal force on a satellite revolving around the Earth is zero. Write the reason.
Answer
The centripetal force and the displacement of the satellite are always perpendicular to each other.
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Question 241 Mark
How much should the speed of an object be increased so that its kinetic energy remains half of the initial kinetic energy?
Answer
$\frac{1}{\sqrt{2}}$ times the initial speed.
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Question 251 Mark
Can the scalar product of vectors be negative?
Answer
The scalar product of two vectors $\vec{A}$ and $\vec{B}$ is $\overrightarrow{ A } \cdot \overrightarrow{ B }= AB \cos \theta$. If the value of $\theta$ is more than $90^{\circ}$ then the value of $\cos \theta$ will be negative corresponding to which the value of $\vec{A} \cdot \vec{B}$ will also be negative.
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Question 271 Mark
The kinetic energies of light and heavy object are equal. Whose momentum will be greater?
Answer
Heavier object will have more momentum because momentum,$
P=\sqrt{2 m E}$
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Question 281 Mark
The work done by the Earth's gravitational force in maintaining the Moon in its orbit (the orbit is considered circular), if it has an elliptical orbit.
Answer
Work W = 0 because displacement is always perpendicular to the applied force. For a complete orbit in an elliptical orbit, W = 0.
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Question 291 Mark
When an arrow is released, from where does it get kinetic energy?
Answer
From the potential energy of the bow.
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Question 311 Mark
Can the entire kinetic energy be dissipated in a completely inelastic collision?
Answer
Yes, when the total momentum of the particles before the collision is zero.
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Question 321 Mark
Can the kinetic energy of a system be converted without converting it into momentum?
Answer
Yes, in inealstic collision.
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Question 331 Mark
Can the kinetic energy of a system remains constant if there is change in the momentum?
Answer
Yes. Since this happens in uniform circular motion.
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Question 341 Mark
What will be the work done by force of gravity in lifting a 10 kg mass to a height of 10 m ?
Answer
Work done by gravitational force
$\begin{aligned}W & =m(-g) h=-m g h
\\& =-10 \times 10 \times 10=-1000 \text { Joule }\end{aligned}$
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Question 351 Mark
Is mechanical energy always conserved?
Answer
No, only in isolated system whereas internal non-conservative force is zero.
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Question 361 Mark
What energy is stored in the spring when the key is inserted in the clock. In what energy does this energy converted when the clock continues to run?
Answer
Potential energy, kinetic energy.
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Question 371 Mark
A porter places a box on the roof of a bus at a height h from the ground. What will be the total work done by the porter and the gravitational field on the box?
Answer
Zero. Since the work done by the porter is equal and opposite to the work done by the force of gravity.
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Question 381 Mark
A porter carried a box on the roof of a bus in 5 minutes. The second porter loaded the same box in 2 minutes. Which porter did more work?
Answer
Both did equal work since the displacement of both is equal.
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Question 391 Mark
A truck and a car are moving on a straight road with equal kinetic energy. If both engines are switched off simultaneously which one will stop at a shorter distance?
Answer
 $\because \frac{1}{2} m_1 v _1^2=\frac{1}{2} m_2 v _2^2$
Here $m_1, v _1$ are the mass and velocity of the truck and $m_2, v _2$ are the mass and velocity of car.
$\begin{array}{l}\because m_1>m_2 \\ \therefore v _1< v _2\end{array}$
$\therefore$ Due to less velocity of the truck, the truck will cover less distance.
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Question 401 Mark
What will be the work done by a man against gravity if he is walking on a plane surface.
Answer
Zero. Since he is moving perpendicular to the force of gravity.
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