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PHYSICS [2 Mark Question Answer]

Energy · ICSE STD 8 (ICSE - English Medium). 20 questions.

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[2 Mark Question Answer]

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20 questions · timed · auto-graded

Question 12 Marks
State two factors on which the work done on a body depends.
Answer
Two factors are :
$(i)$ Magnitude of force applied $(F)$.
$(ii)$ Distance moved by the body in the direction of force $(d)$ or $(5)$
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Question 22 Marks
State the $\text{S.I.}$ unit of work and define it.
Answer
$\text{S.I.}$ unit of work is Joule
Joule “Is that much work done when a force of $\text{IN}$ displaces the body through a distance of lm in the direction of the force.”
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Question 42 Marks
A coolie is moving on a road with a luggage on his head. Does he perform work against the force of gravity? Give reason for your answer.
Answer
No there is no work done against the force of gravity because the displacement and the direction of force are at an angle of $90^\circ$
Explanation:
Walking involves doing the same amount of work against gravity as standing because the weight of the body is the same.
So, the coolie does work against gravity equal to the total weight he is carrying $($his body weight and the weight of whatever he is wearing, carrying, etc$)$.
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Question 52 Marks
In which of the following cases is work being done :
$(a)$ A boy pushing a rock
$(b)$ A boy climbing up the stairs
$(c)$ A coolie standing with a box in his head
$(d)$ A girl moving on the road.
Answer
work being done in the following cases $(b)$ A boy climbing up the stairs
$(d)$ A girl moving on the road.
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Question 62 Marks
Give reasons for the following A teacher moving around in the class is doing work but a child standing and reading a book is not doing any work.
Answer
A child reading a book while standing is not moving from its place i.e. displacement is zero. Hence the product of force and displacement is zero
$W=F \times S$
$W = mg \times O = O$
Hence, the child is not doing any work. Where as teacher is moving from its place is doing work
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Question 72 Marks
Give reasons for the following A horse and a dog are running with the same speed. Which one of them has more kinetic energy than the other.
Answer
A horse has more mass than a dog. As both are running with the same speed.
$M_1$ of the horse is greater than $M_2$ of dog
$\therefore  \text{K.E}$. of the horse is more than $\text{K.E}$. of dog
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Question 82 Marks
State the energy changes that occur in a watch spring while it unwinds.
Answer
A wound$-$up watch spring has potential energy stored in it due to its wound upstate.
The spring $\text{UNWINDS}$ itself, the potential energy changes into $\text{KINETIC ENERGY}$ with which it moves the arms of the watch.
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Question 92 Marks
Can a body possess energy even when it is not in motion? Explain your answer with an example.
Answer
Yes, a body not in motion can possess energy.
Example: Water stored in the dam though not in motion possesses potential energy.
Or
A stone at rest on the top of a building possesses potential energy.
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Question 102 Marks
State two factors on which the kinetic energy of a moving body depends.
Answer
The energy possessed by a body by virtue of its motion is defined as kinetic energy. The factors on which it depends are
$(i)$ Mass of the body.
$(ii)$ Velocity of the body.
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Question 112 Marks
A body of mass $m$ is moved from ground to a height h. If the force of gravity on mass of $1 \ kg$ is $g$ newton, find the force needed to lift the body.
Answer
When a body of mass m at A on the ground is raised above ground through height h at $B$ force is applied. This force applied $=$ weight of body Force on mass $m = F = m g$  Where $\ ‘g\ ’$ is the force of gravity on a mass of $1 \ kg.$
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Question 122 Marks
A bucket full of water is on the first floor of your house and another identical bucket with the same quantity of water is kept on the second floor. Which of the two has greater potential energy?
Answer
As $‘g’$ is constant in both cases and quantity of water $(m)$ is the same in both cases potential energy depends on height. Since the height of the second bucket kept at second floor is greater. Hence, the second bucket at second floor has greater $\text{P.E}.$
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Question 132 Marks
State two factors on which the potential energy of a body at a certain height above the ground depends.
Answer
Potential energy of a body depends on three factors$-$
$1.$ Height of the object from above the ground
$2.$ Mass of the object
$3.$ Gravitational acceleration due to the planet's gravitational force.
Therefore, $\text{P. E}. = m\  ($mass$) \times g\  ($gravitational acceleration$) \times h\  ($height$)$
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Question 142 Marks
What is potential energy ? State its unit.
Answer
POTENTIAL ENERGY : $\text{(P.E}.$ or $U)$
“The energy possessed by a body due to its position above the ground. or change in state.”
UNIT: Unit of $\text{P.E}. = \text{S.I.}$ UNIT OF ENERGY $=$ Joule $(J)$
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Question 152 Marks
What are the two kinds of mechanical energy?
Answer
Two KINDS OF MECHANICAL ENERGY:
$1.$ The Potential energy $\text{(P.E.)}$
$2.$ The Kinetic energy $\text{(K.E.)}$
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Question 162 Marks
How is work related to energy ?
Answer
RELATION BETWEEN WORK AND ENERGY: “Energy is the capacity of doing work” Every form of energy $\rightarrow$ is work.
i.e. work done on the body is stored in the form of energy. Energy is spent when a body does work. Thus to do more amount of work$-$more energy is needed.
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Question 172 Marks
Define $1$ joule of energy.
Answer
$1$ Joule is the amount of work done by a force of $1$ Newton on an object that displaces it through a distance of $1$ meter in the direction of the applied force.
$1 J = 1 N \times 1 m.$
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Question 182 Marks
A body, when acted upon by a force of $10 \ kgf,$ moves to a distance $0.5\  m$ in the direction of force. Find the work done by the force. Take $1 \ kgf = 10 N.$
Answer
$F= 10 \ kgf = 10 \times 10N= 100 N,$
Displacement $S = 0.5\  m$
Work done
$(i)$ When displacement is in the direction of force
$W = F \times S$
$W= 100 \times 0.5 = 50\  J$
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Question 192 Marks
A force of $30 N$ acts on a body and moves it through a distance of $5 m$ in the direction of force. Calculate the work done by the force.
Answer
$F = 30N$
$d= 5m$
Work done $= w = F \times d$
$W = 30 \times 5= 150\  J$
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Question 202 Marks
A pump raises water by spending $4\times 10^5J$ of energy in $10s.$ Find the power of the pump.
Answer
Energy spent $=w=4 \times 10^5 J$
Time taken $=10 s$
Power = Energy $/$ Time
$ P=\frac{4 \times 10^5}{10}=4 \times 10^4 W $
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[2 Mark Question Answer] - PHYSICS STD 8 Questions - Vidyadip