class 12 physics mechanics chapterwise important question ,new syllabus 2078,2079
byDarshan Blogs-
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class 12 physics chapter-wise important question based on the new syllabus
mechanics (each and every question carries 8 marks)
1.(a) Compare the equations of angular
motion with the equations of linear motion. (b) Define angular momentum. (c) A
disc of the moment of inertia 5 x 10-4 kg m2 is rotating freely about
axis o through its center at 40 r.p.m. as shown in Fig. Calculate the new
revolutions per minute (r. p. m.) if some wax of mass 0.02 kg is dropped gently
on to the disc 0.08 m from its axis. [Ans:
32].
2.(a)
Write a relation between the moment of inertia and torque. (b) Describe work and
power in rotational motion. (c) What is the power output in horsepower of an
electric motor turning at 4800 rev/min and developing a torque of 4.30 Nm? Ans:
9.91 W = 0.0133 hp.
3. (a) Define
angular momentum. (b) A planet revolves around a massive star in a highly
elliptical orbit. Is its angular momentum
constant over the entire orbit? (c) A
string is wrapped around the rim of a wheel with a moment of inertia of 0.20 kg m2
and a radius of 20 cm. The wheel is free to rotate about its axis as in Fig.
Initially, the wheel is at rest. The string is now pulled by a force of 20 N.
Find the angular velocity of the wheel after 5.0 seconds.Ans:
100 rad s-1
(a) Describe the work and power in
rotational motion with their expressions. (b) A mass of 2 kg is rotating on a
circular path of radius 0.8 m with an angular velocity of 14 rad s-1. If the
radius of the path becomes 1 m, what will be the value of angular velocity? [Ans: 28.16 rad s-1
The
angular velocity of a wheel increases from 1200 to 4500 rev/min in 10 Compute
its angular acceleration and sec. the number of revolutions during this time.Ans:
117t rad s-2, 475
A wheel starting from rest is rotating with a constant
angular acceleration of 3.0 rad s-2. An observer notes that it traces an angle
of 120 radiations in a 40 sec. interval. For how long the wheel had been
rotated when the observer started his observation?Ans: 8.0 sec
A
disc of mass 2 kg and radius 20 cm is free to rotate about an axis through its
center and perpendicular to the disc. If a force of 50 N is applied
tangentially. Calculate the angular acceleration. Ans: 250 rad s-2
A
constant torque of 20 Nm is exerted on a pivoted wheel for 10 seconds, during
which time the angular velocity of the wheel changes from zero to 100 rpm. When
the external torque is removed, it is stopped by friction in 100 sec. Find (i)
the M.I. of the wheel (ii) the frictional torque (iii) the revolutions made by the wheel in 100s.Ans: (i) 19.09 kg m2 (ii)
2 Nm (iii) 91.67
A
flywheel has a moment of inertia of 4 kg m2 about an axis through its
center and is rotating 120 revolutions per minute. What constant opposing
torque is required to bring it to rest in 5 sec.? Ans•. 10 N
A
disc of the moment of inertia 5 x10-4 kgm2 is rotating freely about axis
I through its center at 40rpm. Calculate the new revolution per minute (r.p.m)
if some wax of mass 0.02 kg is dropped gently onto the disc0.08 m from an axis. Ans: 0.796 rpm
Define a simple pendulum.
What are the drawbacks of a simple pendulum?
A pendulum
clock is taken to the moon. Will it gain or lose time? Can a simple pendulum
experiment be done inside a satellite?
ii what is the relation
between uniform circular motion and S.H.M.?
Suppose a hole
is dug in the earth through its center. A ball is dropped into the hole. Will
the ball return to the thrower? Explain.
A man with a
wristwatch in his hand falls from the top of a tower. Does the watch give the correct time during the free fall?
Define simple
harmonic motion. Find an expression for displacement, velocity acceleration, and
period of a particle describing S.H.M.
What is a simple pendulum?
Show that the motion of a simple pendulum is simple harmonic for small
amplitude. Find an expression for its period.
What are the characteristics
of simple harmonic motion? Derive an expression for the period of such a
motion.
Show analytically that the total energy of a body executing simple harmonic motion is independent of the
position of the body during its motion.
The
amplitude of a particle executing S.H.M. with a frequency of 60 Hz is 0.01 m.
Determine the maximum value of the acceleration of the particle. Ans: 144 m s-2
A small mass of 0.2 kg is suspended from a spring and produces an extension of
0.015 m. The mass is now set into vertical oscillations of amplitude 10 mm.
What is the period of oscillation? Ans: 0.25 s
A small bob of mass 50 g
oscillates as a simple pendulum with an amplitude of 5 cm and a period of 2 s.
Find the velocity of the bob and the tension in the supporting thread when the
velocity of the bob is maximum? Ans: 0.05 m s-1, 0.49 N .
If the potential energy of a particle during
S.H.M. is 2.5J when displacement is half of the amplitude, find the total energy.
Ans: 10 J
A body of mass 0.5 kg suspended by an ideal
spring oscillates up and down. The amplitude of oscillation is 0.5 m and the periodic time is 1.57 seconds. Determine (i) the maximum speed of the body (ii) the maximum kinetic energy (iii) the total (iv) the force constant of the spring.Ans:
(i) 2 m s-1 (ii) 1 J (iii) 1 J (iv) 8 N m-l
The vertical motion of a huge piston in a
machine is approximately simple harmonic with a frequency of 0.5 s-1. A block
of 10 kg is placed on the piston. What is the maximum amplitude of the piston's
S.H.M. for the block and piston to remain together? Ans: 0.99 m
i. A small body of mass 0.1 kg is undergoing S.H.M. of amplitude 1.0 m and period 0.2 s.
(a) What is
the maximum value of the force acting on it? (b) If the oscillations are
produced by a spring, what is the constant m-l of the spring? Ans: 98.7 N,
98.7
(a) State
the law of flotation. (b) Establish the relation between surface tension and
surface energy. (c) Find the work done in blowing a soap bubble of surface
tension 0.06 Nm-l from a 2 cm radius to a 5 cm radius. [Ans: 0.003168 Jl (a)
Describe surface tension and explain its principle. (b) In a surface tension
experiment with a capillary tube, water rises up to 0.1 m. If the same
experiment is repeated on an artificial satellite which is revolving around the
Earth, what will be the height raised in the capillary? Ans:
[Full length of the capillary tube]
(a) Define capillarity and angle of contact.
(b) On what factors does it depend? Where is the angle of contact obtuse, acute, or zero degrees? (c) A raindrop of radius 0.3 mm has a terminal
velocity of 1 m/s in air. The viscosity of air is 18 x Poise. Calculate the viscous
force on the drop. [Ans: 101.73 x 10-9 N]
(a) Differentiate between laminar and
turbulent flow. (b) Describe Reynolds's number. (c) A steel sphere of radius 2 mm
attains a terminal velocity of 0.85 cm s-1 in a liquid at 200 C.
Calculate the viscosity of the liquid at 20 o c. [Density of steel =
8000 kg m-3, density of the liquid 1300 kg m-31. [Ans: 7 N sm-21
(a) Describe
Poiseuillel s formula. (b) Explain the equation of continuity. (c)
Water is flowing steadily through a horizontal pipe of a non-uniform
cross-section. If the pressure of water is 4 x 104 N/m2 at
a point where the cross-section is 0.02 m2 and the velocity of flow is 2
m/s. What is the velocity and the pressure at a point where the cross-section
reduces to 0.01 m2? [Ans; 4 m/s, 3.4 x 104 N/m2 ]
A cube of
wood floating in water supports a 200 g mass resting at the center of its top
face. When the mass is removed, the cube rises 2 cm. Find the volume of the
cube. Ans: 1000 cm3
A cork has a density of 200 kg m-3. What fraction of the volume of the cork
is submerged when the cork floats in water? The density of water = 1000 kg m-3.
Ans: 1/5
Two
capillaries of diameters 02 mm and 0.4 mm
respectively are immersed vertically in water. If water rises to a height of
15.0 cm in the first tube, what is the height of the water column in the
second tube? Ans: 7.5 cm
Water rises in
a capillary tube to a height of 8 cm. Calculate the height to which a liquid
rises in the tube when the tube is immersed in the liquid. [Surface tension of
water is 7.0 x 10-2 N rn-l and that of the liquid
is 5.0 x 10-2. The angle of contact of the liquid is 300 and its density = 800
kg m-3. Ans: 6.2 cm
Two identical drops of water are falling through the air with a steady velocity
of 10 cm s-1. If the drops combine to form a single drop, what would be the
terminal velocity of the single drop? Ans: 15.9 cm s-1.
There is a 1 mm thick layer of glycerine between a flat plate of area 100 cm2
and a big plate. If the coefficient of viscosity of glycerine is 1.0 kg
m-l s-1, then how much force is required to move the plate with a velocity of 7
cm/s? Ans: 0.7 N
Calculate the work done in breaking a drop of
water of 2mm diameter into million droplets of the same size. The surface tension of
water is 72 x 10—3 Nm-l.Ans:
8.96 x 10-5 J
What should be the pressure inside the air bubble of 0.1 mm radius
situated, just below the water surface? The surface tension of water = 7.2 x 10-2
Nm-l and atmospheric pressure = 1.013 x 105
Nm-2. Ans: 1.027 x 105 N rn-2
.
.
the height of the water column in the
second tube? Ans: 7.5 cm
x 10-2 N rn-l and that of the liquid
is 5.0 x 10-2. The angle of contact of the liquid is 300 and its density = 800
kg m-3. Ans: 6.2 cm
Two identical drops of water are falling 
through the air with a steady velocity
of 10 cm s-1. If the drops combine to form a single drop, what would be the
terminal velocity of the single drop? Ans: 15.9 cm s-1.
There is a 1 mm thick layer of glycerine 
between a flat plate of area 100 cm2
and a big plate. If the coefficient of viscosity of glycerine is 1.0 kg
m-l s-1, then how much force is required to move the plate with a velocity of 7
cm/s? Ans: 0.7 N 