24) A ball of mass m moving at speed $v$ collides with a massless spring of spring constant $k$ mounted on a stationary box of mass $M$ in free space. No mechanical energy is lost in the collision. If the system does not rotate, what is the maximum compression $x$ of the spring?

A) $x = v\sqrt{\frac{mM}{(m + M)k}}$

B) $x = v\sqrt{\frac{m}{k}}$

C) $x = v\sqrt{\frac{M}{k}}$

D) $x = v\sqrt{\frac{m + M}{k}}$

E) $x = v\sqrt{\frac{(m + M)^3}{mMk}}$
1. **Conservation of Momentum:**
   When the spring is at maximum compression, the ball and the box move together with a common velocity \( v_2 \). By the conservation of momentum, the initial momentum of the system (ball moving with velocity \( v \) and box at rest) must equal the final momentum of the system (both moving with velocity \( v_2 \)).

   \[
   mv = (M + m)v_2
   \]

   Solving for \( v_2 \):

   \[
   v_2 = \frac{mv}{M + m}
   \]

2. **Conservation of Energy:**
   The initial kinetic energy of the system is entirely due to the ball, as the box is initially at rest. At maximum compression, the kinetic energy of the system is shared between the ball and the box, and the potential energy is stored in the spring.

   Initial kinetic energy:

   \[
   \frac{1}{2}mv^2
   \]

   Final kinetic energy (when both masses move with velocity \( v_2 \)):

   \[
   \frac{1}{2}(M + m)v_2^2
   \]

   Potential energy stored in the spring at maximum compression \( x \):

   \[
   \frac{1}{2}kx^2
   \]

   By conservation of energy:

   \[
   \frac{1}{2}mv^2 = \frac{1}{2}(M + m)v_2^2 + \frac{1}{2}kx^2
   \]

3. **Substitute \( v_2 \) into the Energy Equation:**
   Substitute \( v_2 = \frac{mv}{M + m} \) into the energy conservation equation:

   \[
   \frac{1}{2}mv^2 = \frac{1}{2}(M + m) \left( \frac{mv}{M + m} \right)^2 + \frac{1}{2}kx^2
   \]

   Simplify the kinetic energy term:

   \[
   \frac{1}{2}mv^2 = \frac{1}{2}(M + m) \left( \frac{m^2v^2}{(M + m)^2} \right) + \frac{1}{2}kx^2
   \]

   \[
   \frac{1}{2}mv^2 = \frac{1}{2} \frac{m^2v^2}{M + m} + \frac{1}{2}kx^2
   \]

4. **Isolate the Spring Compression Term:**
   Multiply through by 2 to clear the fractions:

   \[
   mv^2 = \frac{m^2v^2}{M + m} + kx^2
   \]

   Rearrange to solve for \( kx^2 \):

   \[
   kx^2 = mv^2 - \frac{m^2v^2}{M + m}
   \]

   Factor out \( v^2 \):

   \[
   kx^2 = v^2 \left( m - \frac{m^2}{M + m} \right)
   \]

   Simplify the expression inside the parentheses:

   \[
   kx^2 = v^2 \left( \frac{m(M + m) - m^2}{M + m} \right)
   \]

   \[
   kx^2 = v^2 \left( \frac{mM}{M + m} \right)
   \]

5. **Solve for \( x \):**

   \[
   x^2 = \frac{v^2 mM}{k(M + m)}
   \]

   \[
   x = v \sqrt{\frac{mM}{k(M + m)}}
   \]

Thus, the maximum compression \( x \) of the spring is:

\[
\boxed{x = v\sqrt{\frac{mM}{(m + M)k}}}
\]