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PHYSICS [5 Mark Question Answer]

Force and Pressure · ICSE STD 8 (ICSE - English Medium). 3 questions.

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[5 Mark Question Answer]

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Question 15 Marks
Describe an experiment to show that liquid pressure depends on the density of liquid.
Answer
LIQUID PRESSURE DEPENDS ON THE ’DENSITY OF LIQUID : Take two identical balloons attached to one end of each of two identical glass tubes opened at both ends.

Fill tube $(a)$ with milk and tube $(b)$ with alcohol to the same height.
We notice that balloon attached to the tube $(a)$ bulged more than balloon attached to the tube $(b)$. This shows that the same height of milk exerts more pressure than alcohol. Since the density of milk $(1.03)$ is more than density alcohol $(0.8).$
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Question 25 Marks
Match the column
Column $A$ Column $B$
$(a)$ Camel $(1)$ broad and deep foundation
$(b)$ Truck $(2)$ broad feet
$(c)$ Knife $(3)$ six or eight tyres
$(d)$ High building $(4)$ sharp cutting edge
$(e)$ Thrust $(5)$ atm
$(f)$ Moment of force $(6)\  N$
$(g)$ Atmospheric pressure $(7)\  N m$
Answer
Column $A$ Column $B$
$(a)$ Camel broad feet
$(b)$ Truck six or eight tyres
$(c)$ Knife sharp cutting edge
$(d)$ High building broad and deep foundation
$(e)$ Thrust $N$
$(f)$ Moment of force $N m$
$(g)$ Atmospheric pressure $\text{atm}$
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Question 35 Marks
Figure shows a brick of weight $2 \ kgf $ and dimensions $20 \ cm \times 10 \ cm \times 5 \ cm$ placed in three different positions on the ground. Find the pressure exerted by the brick in each case.
Answer
$(a)$ Weight of bricks $=$ Thrust $= F =2 \ kgf$

Area of base $=\frac{20}{100} \times \frac{10}{100}=\frac{1}{50} m ^2$
Pressure exerted $P=\frac{F}{A}=\frac{2 \ kgf }{\frac{1}{50} m ^2}=100 \ kgf /m ^{-2}$
Or
Area of base $=$ area of top $L \times B$
$20 \ cm \times 10=200 \ cm ^2$
$P=\frac{\text { Thrust }}{A}=\frac{2 \ kgf }{200} \ cm ^2=\frac{1}{100}=0.01 \ kg \ cm ^{-2}$

$(b)$ area of base $=$ area of top 
$=5 \ cm \times 10 \ cm =50 \ cm ^2$
 Pressure exerted $=P=\frac{F}{A}=\frac{2 \ kgf }{50 \ cm ^2}=0.04$
$P=0.04 \ kgf \ cm ^{-2}$
$(c)$ Weight of brick
$ F =2 \ kgf $
Area of base $=L \times B$
$ =20 \ cm \times 5 \ cm =100 \ cm ^2 $
Pressure exerted $=\frac{ F }{ A }=\frac{2}{100}=0.02 \ kgf \ cm ^{-2}$
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[5 Mark Question Answer] - PHYSICS STD 8 Questions - Vidyadip