Collision DPP-06

1. Three blocks are initially placed as shown in the figure. Block A has mass m and initial velocity v to the right. Block
B with mass m and block C with mass 4 m are both initially at rest. Neglect friction. All collisions are elastic. The
final velocity of block A is

(A) 0.60 v to the left (B) 1.4 v to the left

2. Two billiard balls undergo a head-on collision. Ball 1 is twice as heavy as ball 2. Initially, ball 1 moves with a speed
v towards ball 2 which is at rest. Immediately after the collision, ball 1 travels at a speed of v/3 in the same direction.
What type of collision has occurred ?
(A) inelastic (B) elastic
(C) completely inelastic (D) Cannot be determined from the information given

3. A ball is dropped from a height h. As is bounces off the floor, its speed is 80 percent of what it was just before, it hit
the floor. The ball will then rise to a height of most nearly
(A) 0.80 h (B) 0.75 h
(C) 0.64 h (D) 0.50 h

4. A ball is thrown vertically downwards with velocity √2𝑔ℎ from a height h. After colliding with the ground it just
reaches the starting point. Coefficient of restitution is
(A) 1/√2 (B) 1/2
(C) 1 (D) √2

5. A ball is projected from ground with a velocity V at an angle  to the vertical. On its path it makes an elastic collision
with a vertical wall and returns to ground. The total time of flight of the ball is
2v sin  2v cos 
(A) (B)
g g
v sin 2 v cos 
(C) (D)
g g

6. In the figure shown, the two identical balls of mass M and radius R each, are placed in contact with each other on the
frictionless horizontal surface. The third ball of mass M and radius R/2, is coming down vertically and has a velocity
= v0 when it simultaneously hits the two balls and itself comes to rest. The each of the two bigger balls will move
after collision with a speed equal to

4v0 2v0
(A) (B)
5 5
v0
(C) (D) none
5

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7. In the above, suppose that the smaller ball does not stop after collision, but continues to move downwards with a
speed = v0/2, after the collision. Then, the speed of each bigger ball after collision is
4v0 2v0
(A) (B)
5 5
v0
(C) (D) none
2 5

8. A metal ball hits a wall and does not rebound whereas a rubber ball of the same mass on hitting the wall the same
velocity rebounds back. It can be concluded that-
(A) metal ball suffers greater change in momentum
(B) rubber ball suffers greater change in momentum
(C) the initial momentum of metal ball is greater than the initial momentum of rubber ball.
(D) both suffer same change in momentum.

9. Before a rubber ball bounces off from the floor the ball is in contact with the floor for a fraction of second. Which of
the following statements are correct –
(A) conservation of energy is not valid during this period
(B) conservation of energy is valid during this period
(C) as ball compressed kinetic energy is converted compressed potential energy
(D) B and C both

10. A block of mass m starts from rest and slides down a frictionless semi-circular track from a height h as shown. When
it reaches the lowest pint of the track, it collides with a stationary piece of putty also having mass m. If the block and
the putty stick together and continue to slide, the maximum stick together and continue to slide, the maximum height
that the block-putty system could reach is

(A) h/4 (B) h/2

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 ANSWER KEY
1. (A)
2. (B)
3. (C)
4. (A)
5. (B)
6. (C)
7. (C)
8. (B)
9. (D)
10. (A)

For any query email us at prayasphysicswallah@gmail.com. You can whatsapp on these numbers from 7 am to 4 pm-7758830689/7840974104.
These numbers is available for calling on the given timings. 7758830689-7 am to 10 am. 7840974104- 10 am to 1 pm.