Final Velocities

Q.

A body of mass 1 kg makes an elastic collision with another body at rest and continues to move in the original direction after collision with a velocity equal to $\frac{1}{4}$ of its original velocity. The mass of the second body is

1. 

2. 

3. 

4. 

Q. Two balls marked 1 and 2 of the same mass m and a third ball marked 3 of mass M are arranged over a smooth horizontal surface as shown in Fig. Ball 1 moves with a velocity $v{­}_1$ towards balls 2 and 3. All collisions are assumed to be elastic. If M <m, the number of collisions between the balls will be

1. One
2. Two
3. Three
4. Four

Q. A body of mass m­₁ moving at a constant speed undergoes an elastic collision with a body of mass $m_2$ initially at rest. The ratio of the kinetic energy of mass $m_1$ after the collision to that before the collision is

1. 
2. 
3. 
4. 

Q. A body of mass $m_1$ moving at a constant speed undergoes an elastic collision with a body of mass $m_2$ initially at rest., the ratio of the kinetic energies of masses $m_2$ and $m_1$ after the collision is

1. 
2. 
3. 
4. 

Q. A ball P of mass 2 kg undergoes an elastic collision with another ball Q initially kept at rest. After the collision, ball P continues to move in its original direction with a speed one-fourth of its original speed. What is the mass of ball Q?

1. 0.9 kg
2. 1.8 kg
3. 1.2 kg
4. 1.5 kg

Q.

Consider a gravity-free hall in which an experimenter of mass 50 kg is resting on a 5 kg pillow, 8 ft above the floor of the hall. He pushes the pillow down so that it starts falling at a speed of 8 ft/s. The pillow makes a perfectly elastic collision with the floor, rebounds and reaches the experimenter's head. Find the time elapsed in the process.

1. 2.88 s

2. 1.22 s

3. 2.22 s

4. 0.22 s

Q. Two perfectly elastic particles P and Q of equal mass travel along the line joining them with velocities 15 m/sec and 10 m/sec in opposite direction. After collision, the velocity of P is and that of Q is respectively (in m/sec).

1. \N
2. 5
3. 10
4. 15
5. 20

Q. The two balls shown in figure are identical, the first moving at a speed $v$ towards right and the second staying at rest. The wall at the extreme right is fixed. Assume all collisions to be elastic.The speeds of the balls remain unchanged after all the collisions have taken place.

1. False
2. True

Q. A heavy steel ball of mass greater than 1 kg moving with a speed of 2 $mse{c}^{-1}$collides head on with a stationary ping-pong ball of mass less than 0.1 gm. The collision is elastic. After the collision the ping-pong ball moves approximately with speed of.

1. 2 m/s
2. 4 m/s
3. $2\times {10}^4$m/s
4. $2\times {10}^3$m/s

Q. A body having velocity of 20 m/s towards +ve x-axis collides with a body initially moving with 10 m/s in -ve x-axis direction. If the collision is elastic and the first body is now moving with a velocity of 15 m/s towards -ve x-axis. The second body must be moving with a velocity of in direction.

1. negative x-axis
2. positive x-axis
3. 5 m/s
4. 15 m/s
5. 20 m/s