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[1 Mark Question Answer]

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22 questions · timed · auto-graded

Question 21 Mark
Define the term moment of force.
Answer
Moment of force — The turning effect of force acting on a body about an axis is called the moment of force.
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Question 31 Mark
Give reason for the following : Two holes are made in a sealed oil tin to take out oil from it.
Answer
Two holes are made in a sealed can so that $\text{ATMOSPHERIC}$
$AIR$ presses the oil at one hole and oil comes out of the second hole.
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Question 41 Mark
Give reason for the following : A balloon collapses when air is removed from it.
Answer
Atmospheric pressure which is more than inside pressure of balloon causes balloon to collapse.
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Question 51 Mark
We do not feel uneasy even under the enormous atmospheric pressure. Give a reason.
Answer
Blood in our body exerts blood pressure which is slightly more than atmospheric pressure and we do not feel uneasy.
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Question 61 Mark
Write the numerical value of the atmospheric pressure on the earth surface in pascal.
Answer
It is about $1.013 \times 10^5 Pa$.
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Question 71 Mark
What do you mean by atmospheric pressure?
Answer
ATMOSPHERIC PRESSURE: “The thrust due to atmospheric air on unit area” is called ATMOSPHERIC PRESSURE.
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Question 81 Mark
A dam has broader walls at the bottom than at the top. Give a reason.
Answer
To withstand the greater pressure of water which increases with increase in depth.
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Question 91 Mark
Which fact about liquid pressure does the diagram in fig. illustrate.
Answer
The figure shows that THE LIQUID PRESSURE INCREASES WITH THE HEIGHT OF THE LIQUID COLUMN ABOVE IT.
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Question 101 Mark
How does the effect of force differ when it is applied on a non$-$rigid body?
Answer
When a force is applied on a non-rigid object it changes interspacing between its constituent particle and causes a change in its dimensions and can produce motion in it.
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Question 111 Mark
How does the effect of force differ when it is applied on a rigid body?
Answer
When a force applied on a rigid object it does not change the interspacing of constituent molecules and does not change dimensions and can cause motion in it.
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Question 121 Mark
A tall building has wide foundations.
Answer
Foundation of buildings are kept wide so that the weight of the building may act on a larger area. As a result, it will exert less pressure on the ground. This avoids sinking of building into the earth.
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Question 131 Mark
Sleepers are used below the rails.
Answer
Sleepers are laid below the rails to reduce pressure $($force/area$)$ on the ground.
$\therefore$ Sleepers increase the area.
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Question 141 Mark
A gum bottle rests on its base. If it is placed upside down, how does the pressure change?
Answer
Lesser area, larger is the pressure.
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Question 151 Mark
A sharp pin works better than a blunt pin. Explain the reason.
Answer
A sharp tip is provided at the end of a pin so that pressure $($FORCE / AREA$)$ exerted by it is maximum when it is pressed by a given force.
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Question 161 Mark
Define force. State its $\text{S.I}.$. unit.
Answer
Force: Force is a physical cause that changes or may tend to change the state of rest or the state of motion of an object. The $\text{S.I}.$ unit of force is Newton.
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Question 181 Mark
What is thrust?
Answer
Thrust is a force or a push. When a system pushes or accelerates mass in one direction, there is a thrust $($force$)$ just as large in the opposite direction.
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Question 191 Mark
A potter turns his wheel by applying a force through the stick near the rim of wheel.
Answer
A potter's wheel has a wheel pivoted at the centre. The potter turns the wheel by means of a stick at the rim of the wheel. He increases the perpendicular distance.
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Question 201 Mark
The spanner $($or wrench$)$ has a long handle.
Answer
Spanner has a long handle to produce larger turning moment and small force is applied at the end of handles.
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Question 211 Mark
What do you mean by the clockwise and anti$-$clockwise moment of force?
Answer
Clockwise moment of force $—$ When the moment of force is in the clockwise direction.
Anticlockwise moment $ —$ When the moment of force acts in an anticlockwise direction.
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Question 221 Mark
State one way to decrease the moment of a given force about a given axis of rotation.
Answer
Either decrease the force or decrease the perpendicular distance of force from the axis of rotation.
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[1 Mark Question Answer] - PHYSICS STD 8 Questions - Vidyadip