# Guys, it's urgent, plz answer them immediately... Q1. A block weighing 1.0 kg is in the shape of a cube of length 10 cm. It is kept on a horizontal table. Find the pressure on the portion of the table where the block is kept. (ans. 1000Pa) Q2. Find the thrust acting on the human body due to atmospheric pressure. Take the surface area of a man of middle size to be 1.5m2and atmospheric pressure (1atm) =1.013 × 105Pa. (ans.15.2 ton wt) Q3. Calculate the mass of a body whose volume is 2 m3and density 0.52 g/cm3. (ans. 1040 kg) Q4. A dining hall has dimensions 50m × 15m × 3.5m. Calculate the mass of air in the hall. Given, density of air =1.30kg/m3. (ans. 3412.5 kg) Q5. A thread of mercury of 10.2 g is in a tube of uniform cross section 0.1cm3. Calculate the length of thread. The density of mercury is 13.6g/cm3. (ans. 7.5cm) Q6. A cubical block of water is dipped completely in water. Each edge of the block is 1cm in length. Find the buoyant force acting on the block. (ans. 10-2N) Q7. A body of mass 2.0 kg and density 8000 kg/m3is completely dipped in a liquid of density 800 kg/m3. Find the force of buoyancy on it. (ans. 2N) Q8. A piece of iron of density 7.8 × 103kg/m3and volume 100 cm3is totally immersed in water. Calculate (a) the weight of the iron piece in air (b) the upthrust and (c) apparent weight in water. (ans. (a) 7.8N (b) 1N (c) 6.8 N) Q9. A solid body of mass 150g and volume 250cm3is put in water. Will the body float or sink. Q10. A solid of density 5000kg/m3weights 0.5 kg in air. It is completely immersed in water of density 1000kg/m3. (a) Calculate the apparent weight of solid in water.(ans. 0.4 kg) (b) What will be its apparent weight if water is replaced by a liquid of density 8000kg/m3? (ans. 0) Q11. The mass of a block made of certain material is 13.5 kg and its volume is 15 × 10-3m3. Will the block float or sink in water. Give reason for your answer. Q12. (a) What is the density of air in NTP? (b)What is the unit of relative density? Q13. (a) When does a body sinks in a fluid? (b)Why does a balloon filled with hydrogen gas rise up against gravity? Q14. (a) Which has greater density: 1 kg of iron or 2 kg of iron? (b)If a hollow sphere and a solid sphere are both made of the same amount of iron, which sphere has greater average density? Q15. (a). A body weighs 10 N in air and 8 N when fully immersed in water. How much is the buoyant force acting on the body? (a) Why are the buoys making the channel in a river are hollow spheres?

Dear Student!!

All the questions are well explained by your friend Rajeev. Please refer the answers posted by Rajeev.

@Rajeev well done !! keep it up!!

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you have ans in the bracket after every Ques.

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plz shorten ur questions

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a) leght of cube= 10cm= 0.1m

area= 0.1m*0.1m

= 0.01m2

..

force= mg

= 1kg*10

=10N

..

pressure= thrust/area

= 10/0.01

= 1000 Pa ans..

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3)  volume= 2m3

density = 0.52 g/cm3= 520kg/m3

mass= volume*density

=2m3* 520kg/m3

= 1040kg ans..

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4) dimensions 50m * 15m * 3.5m.

volume= l*b*h

= 50m * 15m * 3.5m.

= 2625m3

..

density of air =1.30kg/m3

..mass= denstiy * volume

=  1.30kg/m3*  2625m3

= 3412.5kg .. ans. .

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6) the buoyant force acting on an object submerged in a liquid is

F = ρgV

where

ρ is the density of the liquid (here its water so ρ is known)

g is the acceleration due to gravity

and

V is the volume of the submerged object or displaced liquid (= mass/volume)

here,

ρ = 1000 kg/m3

g = 10 m/s2

and V (for cube of 1 cm length) = 1 cm x 1cm x 1cm = 1cm3 = 10-6 m3

thus, we have

F = 1000 x 10 x 10-6 =104* 10-6

or buoyant force will be

F = 10-2

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5) the buoyant force acting on an object submerged in a liquid is

F = ρgV

where

ρ is the density of the liquid

g is the acceleration due t gravity

and

V is the volume of the submerged object or displaced liquid (= mass/volume)

here,

ρ = 800 kg/m3

g = 10 m/s

and V = 2kg / 8000 kg/m3

thus, we have

F = 800 x 10 x 2kg / 8000 kg/m3

or buoyant force will be

F =2 N.. ans..

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this one was 7.. ^_^

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Q8. A piece of iron of and volume 100 cm3is totally immersed in water. Calculate (a) the weight of the iron piece in air (b) the upthrust and (c) apparent weight in water. (ans. (a) 7.8N (b) 1N (c) 6.8 N)

8)   density= 7.8*103kg/m3

volume= 100cm3= 0.0001 m3

mass= density*volume

=  7.8*103kg/m3 *0.0001 m3

= 7.8  *103kg/m3* 10-4 m3

=7.8*10-1kg

..a)weight= mg

=  7.8*10-1kg*10

=7.8N ..

.........

b) upthrust= vdg

where,

v= volume

d= denstiy

and g = accn due to gravity

..

=1000kg/m3  *  0.0001 m3 *10 N

=1N .

c)

density=1000kg/m3

volume= 100cm3= 0.0001 m3

mass= density*volume

=  1000kg/m3 *0.0001 m3

=103kg/m3* 10-4 m3

=10-1kg

..a)weight= mg

=  10-1kg*9.8

=9.8N

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9)A body will float on water if its density is lees than water and will sink in it if its density is greater than water. So, in order to deduce that we need to calculate the density of the object. We know that

density = mass / volume

mass = 150g = 0.15 kg

and volume = 250 cm3 = 250 x 10-6 m3

so,

d = 0.15 / 250 x10-6

or

d = 0.0006 x 10-6 = 600 kg/m3

now, the density of water is 1000 kg/m3. So, as the density of object is less that that of water it will float on it.

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10) a) p= m/V

and w = mg

means. .

V= w/pg

= 0.5kg/5000*10

= 10-5m3

when immered in water mass of liquid displaced,

m = pV= 103*10-5= 10-2

therefore , buoyant force = mg= 10-2*10= 10-1

apparent weight = actual weight - buoyant force

= aparrent weight of solid in water = 0.5- 0.1= 0.4kg ans..

b) simillarly for the liquid of p=8000kg/m3 density., apparent weight can be calculated....

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11) Upthrust = Volume of liquid displaced * density of liquid * g
= 15*10-3 m3 * 103kg/m3 * g
= 15kgf
Since upthrust > weight
The block will float.
While floating, upthrust = weight of block = 13.5kg..

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12)a) NTP (20 degrees, 101.3kPa) 1.205 kg/m3

b) relative density has NO units Because it is the ratio of the density of the material divided by the density of water. So all the units cancel out leaving no units.

It may be simpler to understand if you consider measuring lengths based on, relative to, a stick you have (which, for example, could be 0.8 meter). So if you make a measurement and get a reading of 1.6 meters, then relative to your stick, it is 1.6 meter / 0.8 meter = 2. No units because meter/meter = 1

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13)a) we will sink in a liquid that is less dense.. .

b) hydrogen filled balloon tends to go up ward towards exosphere against the force of gravity. Its movement is totally based on the density difference of the medium(air) and the object(balloon) not due to force of gravity because gravity does not explain us this type of behavior, if we release this balloon in exosphere it will suspend in exosphere because the densities of both (balloon and exosphere) are the same. ..

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14) a) 2kg of Iron..

b) a solid shpere..

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15)

Q15. (a). A body weighs 10 N in air and 8 N when fully immersed in water. How much is the buoyant force acting on the body?

weight= 10N

w=mg

= m= w/g

= m= 10N/10m/s2

= m = 10kg

....

density= mass/volume

density of water = 1000kg/m3

mass of body= 1kg

volume= mass/density

= 1kg/ 1000kg/m3

= 0.001m3

..

buoyant force= vdg

v= volume

d= density

and g= accn due to grvity

= 0.001m3*1000kg/m3*10m/s2

= 10N ans..

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