To find the elongation in the spring, let's analyze the forces acting on the system under equilibrium conditions. Here's the step-by-step approach:

Assumptions and given values:

1. The spring constant ($k$) = 400 N/m.
2. All surfaces are smooth, so friction is neglected.
3. Pulleys and strings are ideal, implying no energy loss and perfect transmission of forces.
4. The system is in equilibrium.

Equilibrium Conditions:

• The forces in the system must balance because the system is at equilibrium.
• The spring elongation, $\Delta x$, is determined by the balance of forces exerted by the weights attached to the string and the restoring force of the spring.

Restoring Force of the Spring:

The restoring force exerted by the spring is: $F_{\text{spring}} = k \Delta x$

Force Balance:

The weights of the blocks connected to the string create tension in the string, which is transmitted through the system. Assume the total tension force in the string is $T$.

Equating the tension force to the spring force (since the spring is extended due to this tension): $T = k \Delta x$

If the mass connected to the string produces a gravitational force of $mg$, the equilibrium condition becomes: $mg = k \Delta x$

Elongation Calculation:

$\Delta x = \frac{mg}{k}$

Conversion to cm:

The elongation in the spring ($\Delta x$) is usually asked in cm. Convert the result from meters by multiplying by 100.

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If you can provide the masses of the blocks connected or further details about the system configuration (like specific block weights), I can compute the exact elongation in the spring. Would you like to provide additional data or confirm the assumptions?