MCQ Questions for Class 8 Physics Force And Pressure Quiz 7

Q.1.

If a body is moving with a constant speed along a straight line; then in order to change its direction of motion, an external force has to be applied in a direction normal to the direction of motion.

50%
True
50%
False

Explanation

Q.2.

Pressure varies inversely with area (A) provided the thrust is same.

50%
True
50%
False

Explanation

pressure =

\frac{t h r u s t}{a r e a}

$\dfrac{thrust}{area}$

So if thrust is the same then pressure varies inversely with the area.

So option (A) is correct

Q.3.

Pressure varies with force (F) as (provided area is same)

50%
$P\propto F$
50%
$P\propto \dfrac {1}{F}$
0%
$P\propto F^2$
0%
$P\propto \dfrac {1}{F^2}$

Explanation

We know, Pressure is the force exerted divided by area.

Pressure

= \frac{f o r c e}{A r e a},

$=\dfrac{force}{Area},$ When A is consfont,

Pressure is directly proportional to F. ie

P \propto F

$P\propto F$

Hence, Option A

Q.4.

A force produces translational motion:

50%
When the body is free to move and applied force pass through the rotation axis
0%
When the body is hindered to move
0%
When the body is rigidly fixed
50%
When the body is free to move and applied force does not pass through the rotation axis

Explanation

Q.5.

Which of the following force doesn't change with distance?

0%
Electrostatic force
0%
Gravitational force
100%
Frictional force
0%
Magnetic force

Explanation

Q.6.

It is better to use a sharp tipped nail than a blunt nail because :

100%
The tip with the smallest area will produce a higher pressure when a force is applied.
0%
A sharp tipped nail needs a larger force to drive it into the wooden surface
0%
The sharp tip saves cost as less raw materials are required to make such nails
0%
The sharp tip has a spiralling effect when the nail is hit on the head

Explanation

Q.7.

With the increase in the area of contact of an object, the pressure:
(Note : Thrust remains same)

0%
Increases
100%
Decreases
0%
Is not affected
0%
None of these

Explanation

Since,

P = \frac{F}{A}

$P = \frac{F}{A}$
Thus pressure is inversely proportional to area,

i . e . P \propto \frac{1}{A}

$i.e. \,\,P \propto \frac{1}{A}$

With the increase in the area of contact of an object the pressure decreases because pressure is inversely proportional to area of contact.

Q.8.

Which of the statements about force are true?

0%
It can be seen
100%
It causes an object to move
0%
It is pull or a push
0%
It can change the motion of an object

Explanation

Q.9.

The pressure exerted by a women wearing shoes with pointed heels is ...... than what an elephant with one foot can exert on ground :

0%
Much lesser
100%
Much greater
0%
Both equal
0%
None of these

Explanation

Q.10.

Fill in the blank.

Dams are ____ at the base.

100%
thicker
0%
thinner
0%
same
0%
can't say

Explanation

P r e s s u r e = \frac{F o r c e}{A r e a}

$Pressure=\frac{Force}{Area}$

So pressure is inversely proportional to area of contact.

That is why area at base of dam is more as compared to the top so there is less pressure on base so it will be safe.

Q.11.

Which of the following has infinite range?

0%
Gravitational force
0%
Electromagnetic force
100%
Strong nuclear force
0%
Both a and b

Explanation

Q.12.

The same force acting on a smaller area exerts a larger pressure, and a smaller pressure on a larger area.

100%
True
0%
False
0%
Ambiguous
0%
Data insufficient

Explanation

Q.13.

A box exerts a force of

420 N

$420N$ on a floor. The bottom of the box has an area of

0.7 m^{2}

$0.7m^2$ . What is the pressure exerted by the box on the floor?

0%
$600 Pa$
0%
$500 Pa$
0%
$400 Pa$
0%
$700 Pa$

Explanation

Given, force,

F = 420 N

$F=420N$ ; area

= 0.7 m^{2}

$=0.7m^2$ ;
Pressure,

P = ?

$P=?$
Pressure,

P = \frac{F o r c e}{A r e a} = \frac{F}{A} = \frac{420}{0.7} = 600 P a

$P=\displaystyle\frac{Force}{Area}=\frac{F}{A}=\frac{420}{0.7}=600Pa$

Q.14.

Ask a friend to drive a small nail into a piece of wood placed on top of a pile of books on your head. Why doesn't this hurt you?

0%
Because the nail has a sharp point and thus, exert less pressure on wood
0%
The force is exerted on the wood, thus it has no effect on out head
0%
The relatively large mass of the books and block on your head resists being moved
0%
Action-reaction forces cancel out each other

Explanation

Q.15.

A force

F_{1}

$\displaystyle F_{1}$ accelerates a particle from rest to a velocity v. Another

F_{2}

$\displaystyle F_{2}$ decelerates the same particle from v to rest, then:

0%
$\displaystyle F_{1}$ is always equal to $\displaystyle F_{2}$
0%
$\displaystyle F_{2}$ is greater than $\displaystyle F_{1}$
0%
$\displaystyle F_{2}$ may be smaller than, greater than or equal to $\displaystyle F_{1}$
0%
$\displaystyle F_{2}$ cannot be equal to $\displaystyle F_{1}$

Explanation

Q.16.

Porters (coolies) place a round piece of cloth on their heads, to ______ the area of contact of the load with their head.

0%
increase
0%
decrease
0%
maintain the same
0%
Cannot say

Explanation

Q.17.

It is easier to cut with a sharp knife than with a blunt one, This is because

0%
sharp knife exerts more pressure
0%
sharp knife exerts less pressure
0%
both knives exert equal pressure
0%
sharp knife has a better grip

Explanation

Q.18.

Buildings have wide foundations so that they exert less force on the ground or Earth.

0%
True
0%
False

Explanation

The force exerted by the building on the ground,

F = m \times g

$F=m\times g$

where,

m = m a s s

$m=mass$ and

g = a c c e l e r a t i o n d u e t o g r a v i t y

$g= acceleration\ due\ to\ gravity$

Force does not depend on the area.

We know,

P r e s s u r e = \frac{f o r c e}{A r e a}

$Pressure=\dfrac{force}{Area}$

Buildings have wide foundations so that they exert less pressure on the ground or Earth.

Q.19.

A

1.5 m

$1.5m$ wide by

2.5 m

$2.5m$ long water bed weighs

1025 N

$1025N$ . Find the pressure that the water bed exerts on the floor. Assume that the entire lower surface of the bed makes contact with the floor.

0%
$273.3Pa$
0%
$373.5 Pa$
0%
$173.3Pa$
0%
$473.3Pa$

Explanation

Pressure exerted by water bed will be force applied per unit area.

P = \frac{F}{A}

$P=\dfrac {F}{A}$

Given:

Force=

1025 N

$1025 \ N$

Area=

1.5 m \times 2.5 m = 3.75 m^{2}

$1.5 m \times 2.5m = 3.75 m^2$

Pressure

= \frac{1025 N}{3.75 m^{2}} = 273.3 N / m^{2} = 273.3 P a

$=\dfrac { 1025 \ N }{ 3.75 \ m^2} =273.3 \ N/m^2 = 273.3 \ Pa$

Q.20.

Which of the following is NOT true?

0%
A sharp knife can easily cut due to its small cutting surface.
0%
It is easier to walk in sand than on road.
0%
A battle tank can move easily on soft ground because its tracks have bigger surfaces.
0%
The pressure exerted by a needle is much more than the foot of an elephant.

Explanation

Q.21.

State whether the given statement is TRUE or FALSE.

The foundations of high-rise buildings are kept wide so that they may exert more pressure on the ground.

0%
True
0%
False

Explanation

We know,

Pressure = \frac{Thrust}{Area}

$\text{Pressure}=\dfrac{\text{Thrust}}{\text{Area}}$

So, if the area of contact increases then the pressure reduces.

Wide foundations exert lesser pressure because the increase in the area of contact reduces the pressure on the ground and the buildings will not sink.

So the statement is False.

Q.22.

Force can only increase or decrease the speed of a moving object or change its direction.

0%
True
0%
False

Explanation

Q.23.

State whether the given statement is TRUE or FALSE.

A liquid in a container exerts pressure in all directions- on the bottom of the container, on its walls, and even upwards.

0%
True
0%
False

Explanation

Q.24.

Tick the correct statements.

0%
air exerts pressure because it occupies space and has weight.
0%
air is more dense near the earth. It goes on thinning out as we go up.
0%
oxygen content of the air goes on decreasing as we go up.
0%
air is uniformly dense right fron the earth to the sky.
0%
air pressure is very high near the earth and it goes on decreasing as we go up.
0%
$99\%$ of air exists up to a height of nearly $30\;km$ .

Explanation

The air around you has weight, and it presses against everything it touches. That pressure is called atmospheric pressure, or air pressure. It is the force exerted on a surface by the air per unit area of surface Atmospheric pressure is commonly measured with a barometer.

Earth's gravity pulls air as close to the surface as possible.Hence more air molecules are present near the surface of earth hence density of air is more at surface and decreases as we go up.Pressure is directly proportional to density hence pressure is also maximum at surface and goes on decreasing as we go up.For the same reason oxygen decreases as we go up because total air is decreasing hence oxygen which is nearly

20

$20$ percent of air also decreases.

Because of earth's attraction most of air is present within

30 k m

$30km$ from earth surface. In figures, nearly 99% of air exists up to a height of nearly 30km.

Q.25.

A mountain climber experiences a nose bleed due to:

0%
Decrease in atmospheric pressure
0%
Increase in atmospheric pressure
0%
More gravitational pull
0%
Effect of high altitude

Explanation

Q.26.

If we apply the brakes to a moving car, it comes to rest. This shows that force can make a moving object go slower.

0%
True
0%
False
0%
Ambiguous
0%
Data insufficient

Explanation

Q.27.

A contact force cannot act through

0%
Empty space
0%
Touching
0%
Touching with a metal rod
0%
Touching with a wooden rod

Explanation

Q.28.

(a) A force of

200 N

$200\;N$ acts on an area of

0.02 m^{2}

$0.02\;m^2$ . Find the pressure in Pascal.
(b) What force will exert a pressure of

50, 000 P a

$50,000\ Pa$ on an area of

0.5 m^{2}

$0.5\;m^2$ ?
(c) Find out the area of a body which experiences a pressure of

500 P a

$500\ Pa$ by a force of

100 N

$100\;N$ .

0%
(a) $\;10000\;Pa$ , (b) $\;25000\;N$ , (c) $\;0.2\;m^2$
0%
(a) $\;1000\;Pa$ , (b) $\;2500\;N$ , (c) $\;2\;m^2$
0%
(a) $\;100000\;Pa$ , (b) $\;250000\;N$ , (c) $\;0.2\;m^2$
0%
(a) $\;100\;Pa$ , (b) $\;250\;N$ , (c) $\;0.2\;m^2$

Explanation

We know

P r e s s u r e (P) = \frac{F o r c e (F)}{A r e a (A)}

$Pressure(P)=\dfrac{Force(F)}{Area(A)}$

(a)

F = 200 N

$F=200N$

A = 0.02 m^{2}

$A=0.02m^2$

P = \frac{200}{0.02} = 10000 P a

$P=\dfrac{200}{0.02}=10000Pa$

(b)

P = 50000 P a

$P=50000Pa$

A = 0.5 m^{2}

$A=0.5m^2$

F = P A = 50000 \times 0.5 = 25000 N

$F=PA=50000\times 0.5=25000N$

(c)

P = 500 P a

$P=500Pa$

F = 100 N

$F=100N$

A = \frac{F}{P} = \frac{100}{500} = 0.2 m^{2}

$A=\dfrac{F}{P}=\dfrac{100}{500}=0.2m^2$

Q.29.

Which of the following class of force is different from others?

0%
Magnetic force
0%
Electrical force
0%
Gravitational force
0%
Stretching of a spring

Explanation

Q.30.

a

$a$ . To stretch the bow, the archer applies a force that causes a change in its ______

b

$b$ . The force applied by the archer to stretch the bow is an example of ______ force.

c

$c$ . The type of force responsible for a change in the state of motion of the arrow is an example of a _____ force.

d

$d$ . While the arrow moves towards its target, the forces acting on it are due to ______ and that due to _______ of air.

0%
Shape
0%
Muscular
0%
Contact
0%
Gravity, Friction

Explanation

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