send me the numericals from gravitation chapter from NCERT.All numericals.With answer
Answers
Question 1.
A piece of iron weighs 44.5gf in air, 39.5 gf in water and 40.3 gf in an oil. Find:
a.the relative density of iron.
b. the density of oil in SI unit. What assumption have you made in your calculation?
Given density of water=1 gm/cc = 1000 kg/cubic m
Answer Method -1
a. Let V be the volume of iron and ρi be the density of Iron,ρo be the density of oil
Upthrust in Water = 44.5 - 39.5 = 5 gf =.049 N
Now
V×1000×9.8=.049
or V=.000005m3=5cm3
Now mass of Iron=44.5 gm
Density of Iron = 44.5/5 = 8.9 g/cc
Now relative density of the iron = Density of iron /Density of watter = 8.9/1 = 8.9
b. Now Upthrust in oil = 44.5 - 40.3= 3.2 gf= .03136 N
Now
V×ρo×9.8=.03136
or ρo=640kg/m3
Method-2
a. This can be calculated using the formula
Relativedensityofsolid=
Weightofsolidinair
Lossofweightofsolidinwater
=
44.5
5
=8.9
b. This can be calculated using the formula
Relativedensityofoil=
Lossofweightofsolidinoil
Lossofweightofsolidinwater
=
3.2
5
=.64
Density of Oil =.64 X 1000 = 640 kg/cubic mv
Question 2.
A solid weighs 200 gf in air, 160 gf in water and 170 gf in a liquid. Calculate the relative density of the solid and that of the liquid?
Answer a. This can be calculated using the formula
Relativedensityofsolid=
Weightofsolidinair
Lossofweightofsolidinwater
v =
200
40
=5
b. This can be calculated using the formula
Relativedensityofliquid=
Lossofweightofsolidinliquid
Lossofweightofsolidinwater
=
30
40
=.75
Question 3.
What do you understand by 1 Pascal and 1 Newton?
Answer Pascal is the SI unit of Pressure and it is defined as 1 Newton force or thrust on 1m2 of Surface area
Newton is the SI unit of Force. it is the amount of force the will accelerate a mass of 1kg to 1m/s2.
Question 4.
Define thrust. A force of 150N acts on a surface of area 15cm2. Calculate thrust and pressure?
Answer The force acting on an object perpendicular to the surface is called thrust
Thrust =150 N
Now Pressure=
thrust
SurfaceArea
=
150
15×10−4
=105N/m2
Question 5.
If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and then floats. Why?
Answer The salt solution has much more density then the plain water solution.Now the density of salt solution is more than egg,so egg begins to float
Question 6.
Define pressure? Give its mathematical expression and its SI unit?
Answer The thrust on unit area is called pressure.
Pressure=
thrust
SurfaceArea
Its SI unit is Pascal
Question 7.
In what direction does the buoyant force on an object immersed in a liquid act?
Answer Upward direction
Question 8.
Differentiate between density and relative density?
Answer Density: Mass per unit volume of a substance is called density. SI unit is kg/m3
density=
mass
volume
Relative Density: The ratio between density of a substance and density of water is called relative density.Relative density has no units because it is the ratio between the similar physical quantities
Relativedensity=
densityoftheobject
densityofwater
Question 9.
Relative density of gold is 19.3. The density of water is 1000kg/m3. Find the density of gold in SI unit in g/cc?
Answer 1000kg/m3=1g/cm3
Relativedensity=
densityofthegold
densityofwater
or
densityofgold=(Relativedensity)×(densityofwater)=19.3g/cc
Question 10.
Two objects of masses m1 and m2 having the same size are dropped simultaneously from heights h1 and h2 respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if
(i) one of the objects is hollow and the other one is solid
(ii) bothof them are hollow, size remaining the same in each case. Give reason?
Answer