KENDRIYA VIDYALAYA, SULUR
WINTER BREAK ASSIGNMENT
SUBJECT: PHYSICS (XI)
1. Find 1 Kg m2 s-2= …………. G cm2 s-2. (1)
2. Given a+b+c+d=0, can we say a,b,c,d, must be a
null vector. Give example.(1)
3. A particle of mass 5000 gm is pulled along a smooth
horizontal surface by a horizontal spring. The
acceleration of the particle is 10ms-2. Find the tension
in the string.(1)
4. What should be the angle between the force and the
displacement for maximum and minimum work? (1)
5. When a body is said to be weightlessness? Give
reason(1)
6. The gravitational force between two spheres is x when
the distance between their centers is y. what will be
the new force if the separation is made 3y.
(Or)
Two satellites of masses 3 m and m orbit the earth in
circular orbits of radii r and 3 r respectively. What is the
ratio of their orbital speeds? (2)
7. An electron of mass 9x 10-31 kg revolves in a circle of
0.53 A0 around the nucleus of hydrogen atom with a
velocity of 2.2x106 ms-1. Find the angular momentum
of the electron about the centre of the circle. (2)
8. A gardener moves a lawn roller through a distance of
50 m with a force of 50N inclined at an angle of 600 to
the direction of motion. calculate his wages if he is
paid 20 paisa for doing 25 J of work(2)
9. A particle moves with a constant angular speed of
certain radius r and is acted upon by a certain
centripetal force F. If the angular speed is doubled ,
keeping the radius the same, what will be the new
centripetal force.(2)
10. A cyclist completes one round of circular track of
radius R=20m in 20seconds. what will be the distance
and displacement at the end of 40 seconds and 50
seconds.(2)
11. The force experienced by a mass moving with
uniform speed v in a circular path of radius r
experiences a force which depends on its mass, speed
and radius. Prove that f=mv2/r. (3)
12. The radius of the earth is 6.37x10-6 m and its
average density is 5.517x103 kg m-3. Calculate the
mass of earth to correct significant figures.
(or)
Find the value of 60 watts on a system having 100g,
20cm and 1 minute as the fundamental units. (3)
13.A drunkard walking in a narrow lane takes 5 steps
forward and 3 steps backward, followed again by 5 steps
forward and 3 steps backward, and so on. Each step is 1 m
long and requires 1 s. Plot the x-t graph of his motion.
Determine graphically and otherwise how long the drunkard
takes to fall in a pit 13 m away from the start. (3)
14.A body is moving in a straight line along X axis. Its
distance x in meters from the origin is given by x=8t-3t2,
the time t is in seconds .Find the average speed of the
body in time interval t=0 sec to t= 1 sec. (3)
15.Prove that the maximum horizontal range is four times
height attained by the projectile (3)
16.Draw the graph i) between momentum P and velocity V
keeping mass m as constant. Ii)P versus m ,keeping V
constant iii) V versus m, keeping P constant (3)
17.Show that Newton’s second law of motion is the real law
of motion(3)
18.State and prove work energy theorem. Discuss i)if net
force does positive work , what happens to kinetic energy
ii) if net force does negative work , what happens to
kinetic energy iii) if net force does zero work , what
happens to kinetic energy (3)
19.Define centre of gravity. Show that for an isolated system
the centre of mass moves with a uniform velocity along a
straight line path.(3)
20.Define moment of inertia. State parallel and
perpendicular axis theorems.(3)
21.Name the physical quantity corresponding to force in
rotational motion. How it is related to force and give its
unit. Find the torque of a force 7i-3j-5k about the origin
which acts on a particle whom position vector is i+j-k
(3)
22.Define weight. A body is taken from the center of the
earth to the moon. What will be the changes in the
weight of the body? i) at the centre of earth. Ii) centre to
surface of earth iii) at the surface of earth iv) from
surface of earth to one place where gravitational
attractions of earth and moon are equal and opposite v)
beyond this up to moon (3)
23.Ram a student of class VI was going on foot with his
grand father on a road. On the way, Ram observed that
when the road is turning in a circular mode, the inner
side of the road is inclined slightly inwards and a motor
cyclist was also inclined inwards which is passing through
that turn. Ram got surprised and asked his grand father
who is a retired science teacher that why did the cyclist
not fall from the motor cycle when he inclined inner
wards. His grand father explained him centripetal and
centrifugal forces when the body is moving in a circular
path.
i)
What are the values that Ram displayed
ii)
Define centripetal force
iii) A cyclist speeding at 18 Km/hr on a level road takes
a sharp circular turn of radius 3 m without reducing
speed. The coefficient of static friction is 0.1. Will the
cyclist slip while taking a turn? (4)
24.A) i) State and prove parallelogram law of vectors .
ii) The resultant of two equal forces acting at right
angles
to each other is 1414 N. Find the magnitude of each
force.
(or)
B) Show that vector addition obeys i) commutative law
ii) Associative law. (5)
25. A) Prove that kinetic energy =1/2 (mv2) and potential
energy =mgh
B) What is the running speed of a pole vaulter who clears
a bar of 5m ?
(Or)
A) Discuss on inelastic collision in two dimensions with
figure.
B) i) A light body and a heavy body have the same
momentum. Which one has larger kinetic energy?
ii) i) A light body and a heavy body have the same
kinetic energy. Which one has larger momentum?(5)
26.
A) What is a satellite? Derive expressions for orbital
velocity and period of revolution of satellite above the
surface of earth.
(or)
B) i) Define gravitational potential energy and Show that its
equals to –GMm/r where the symbols have their usual
meaning.
ii) If a body is moved away from the earth, does its
gravitational potential energy decreases or increases.
Iii) The gravitational potential energy of a body near
earth surface is negative. What does it mean? (5)
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11 PHYSICS ANSWER KEY
1
10 7.
2
No, even a+b=0 etc
3
50 N
4
0 0 and 90 0.
Free fall
5
6
F∞1/r 2. New force= x/9.
(or)
V=√(GM/r), v1/v2=√r2/r1=√3.
7
L=mvr, =1.0494x10-34 Js
8
W=FS CosѲ=1250J, wages=(0.2x1250)/25=Rs 10
9
F=mr2, F’=m(2)2r, F’=4F.
10
Displacement i) o and ii) 40m
Distance i)2x2x3.14x20=251.2m
ii)2.5x2x3.14x20=314m
11
Coeff a=1,b=2,c=-1.
12
M=vxd=4/3x3.14x(6.37x106)3x5.517x103=5.97x1024
kg
(or)
N2=60(M1/M2)1 (L1/L2)1 (T1/T2)-3=3.24x109 units.
13
37 sec
14
V=dx/dt=8-6t, at t=0, u=8 m/s,at t=1, v=2 m/s,
av.sp=(8+2)/2=5 m/s
15
Rmax=v02 sin 2Ѳ/g=v02 sin 2x45=v02/g
Hmax=v02sin2Ѳ/2g=v02sin2 450/2g=v02/4g, Rmax=4 h
max.
16
450 inclinedi) and ii) and iii) parabola i) and ii) P y
axis, iii) v isin y axis.
17
I) a=F/m, a=0 if F=0
ii)if Fext =0, ΔP=0,FAB x t + FBA x t = 0, FAB=-FBA
18
19
Here dw=f.ds=ma .ds= mvdv, w=∫𝑣0 𝑚𝑣 𝑑𝑣 = 𝛥𝐾. 𝐸
i)K.E> ii)K.E < iii)K.E remains same.
Define+F=m d/dt (v cm)=0, v cm is constant
20
state
21
Torque, τ=r X F, Nm. Ii)τ= 2i+12j+10k
22
Define, i) 0 ii)increases iii) max iv) 0 v)due to
moons gr.atttr. weight increases.
23
I) learner etc ii)force towards centre etc iii)v2 < µ
g= 0.1x3x9.8=2.94 m2/s2
Speed of cyclist=18 km/hr=5 m/s, v2= 25 m2/s2,
cclist will slip.
24
Ii)R= (p2+Q2+2PQ cos Ѳ)1/2, R= √2P, P=Q=1000N
25
Ii)V=√2gh=7√2 m/s
B) i) lighter body k= p2/2m
ii) heavy body
26
(or)
ii) Increases
iii)it means work is done by gr. Force as body
moves towards earth.
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s
R