Question:medium

A sphere of mass m moving with constant velocity u hits another stationary sphere of the same mass. If e is the coefficient of restitution, the ratio of velocities ($v₁/v₂$) after collision will be:

Show Hint

For equal masses, $v₁ = \frac1-e2u$, $v₂ = \frac1+e2u$.
Updated On: May 24, 2026
  • $\frac1-e1+e$
  • $\frac1+e1-e$
  • $\frace+11-e$
  • $\frace-1e+1$
Show Solution

The Correct Option is A

Solution and Explanation

To solve this problem, we need to apply the principles of conservation of linear momentum and the concept of coefficient of restitution after the collision between two spheres.

Principles and Explanation:

  • Conservation of Linear Momentum: In the absence of external forces, the total linear momentum before and after the collision is conserved.
  • Coefficient of Restitution (e): It is defined as the relative velocity of separation divided by the relative velocity of approach. Mathematically, \(e = \frac{v_2 - v_1}{u - 0}\), where \(v_2\) and \(v_1\) are the velocities of the two bodies after the collision.

Step-by-step Solution:

  1. Consider two spheres, sphere A and sphere B, both having mass \(m\). Sphere A is moving with velocity \(u\), and sphere B is stationary.
  2. From the conservation of linear momentum: \(mu = mv_1 + mv_2\) 
    Simplifying, we have: \(u = v_1 + v_2\) (Equation 1)
  3. The coefficient of restitution is given by: \(e = \frac{v_2 - v_1}{u}\) 
    Simplifying this, we get: \(v_2 - v_1 = eu\) (Equation 2)
  4. Adding Equation 1 and Equation 2: \(u + v_2 - v_1 = v_1 + v_2 + eu\) 
    Simplifying gives: \(2v_2 = u(1 + e)\) 
    Therefore: \(v_2 = \frac{u(1 + e)}{2}\)
  5. Substituting the value of \(v_2\) in Equation 1: \(u = v_1 + \frac{u(1 + e)}{2}\) 
    Solving for \(v_1\): \(v_1 = \frac{u(1 - e)}{2}\)
  6. Now, the ratio of velocities after collision is: \(\frac{v_1}{v_2} = \frac{\frac{u(1 - e)}{2}}{\frac{u(1 + e)}{2}}\) 
    Simplifying, we get: \(\frac{v_1}{v_2} = \frac{1 - e}{1 + e}\)

Thus, the ratio of the velocities \(v_1/v_2\) after the collision is given by \(\frac{1-e}{1+e}\). The correct option is:

\(\frac{1-e}{1+e}\)

Was this answer helpful?
0