pl answer Q 21 21. A rocket, with an initial mass of 1000kg, is launched vertically upwards from rest under
The rocket burns fuel at the rate of 10 kg per second. The burnt matter is ejected vertically
wards with a speed of 2000m/s relative to the rocket. If burning ceases after one minute, the
mum velocity of the rocket is (154 x). Find x. (g = 10mjs2)
22. A bullet of mass 20gm travelling horizontally with a speed of 500m/s passes through a
block of 10kg initially at rest on a level surface. The bullet emerges with a speed of
and the block slides 20cm on the surface before coming to rest. Then coefficient of friction
tween the block and the surface is (0.04)n. The value of n is
23. A gun is mounted on a railroad car. The mass of the car, the gun the shells and the operator is
where m is the mass of the one shell. If the muzzle velocity of shell is 200m/s, the recoil speed
rn./s. Find ?
Car after second shot is 200 — + —
24. A sphere strikes a wall and rebounds with coefficient of restitution 1/3. If it rebounds with
velocity of 0.1m/sec at angle of 600 to the normal to the wall, the loss of K.E is . What is
value of k ?
25. Three objects A, B and C are kept in a straight line on a friction less horizontal surface. These have
masses m, 2m and m respectively. The object A moves towards B with a speed 9m/s and makes
elastic collision with it. Thereafter B makes completely inelastic collision with C. All motions
on the same straight line. Find the final speed (in m/s) of object C
6)AB 7)AD 8)AD 10)C
14)A 15)A-Q; B-R;C-S; D-P
l. particles of masses and and velocities and 0), make an elastic head on collision"
If the initial kinetic energies of the two particles are equal and m, comes to rest after collision'
2. blocks A and B, each of mass m, are connected by a massless spring of natural length
spring constant K. The blocks are initially resting on a smooth horizontal floor with the spring
natural length as shown in the figure. A third identical block C, also of mass m, moves on
with a speed v along the line joining A and B and makes a perfectly elastic collision with A. TV