Final answer:
The height y is approximately 2.91 meters.
Step-by-step explanation:
To find the height y when a stationary block falls onto a spring, we can use the principle of conservation of mechanical energy. At the highest point of the fall, the block has only potential energy, which is converted to elastic potential energy when it compresses the spring.
The equation that relates potential energy and spring potential energy is
mgh = (1/2)kx^2,
where m is the mass of the block, g is the acceleration due to gravity, h is the height, k is the spring constant, and x is the maximum compression of the spring. In this case, the mass of the block is 2 kg, the spring constant is 400 N/m, and the maximum compression is 3 m. Substituting these values and solving for h, we get:
h = \frac{(1/2)kx^2}{mg}
h = \frac{(1/2)(400 N/m)(3 m)^2}{(2 kg)(9.8 m/s^2)}
h \approx 2.91 m
Therefore, the height y is approximately 2.91 meters.