A block of mass 25 kg is sitting on a platform as shown in the figure below. The

Question

A block of mass 25 kg is sitting on a platform as shown in the figure below. The platform sits on a spring with K=2600 N/m. The mass is initially at rest.

(a) If the platform is depressed a distance 0.80 m and held there, what is the mechanical energy of the system? (For this question and the remaining questions, let y=0 be at the position where the spring is fully compressed.)

(b) The platform is then released, and the mass moves upward and eventually flies off the platform. Assume the spring returns to its relaxed state (unstretched and uncompressed) after the mass leaves the platform. What are the kinetic energy, gravitation potential energy, and elastic potential energy of the system when the mass reaches its highest point?

(c) How high with the block go? Measure the distance from the height of the uncompressed platform.

Explanation / Answer

a. if we take initial mechanicl enegy = U J
then after compression ME = U - mg(0.8) + 1/2 k (0.8)^2

ME = U - 196.2 + 832 = U + 635.8 J

b. compression = 0

   elastic potential energy = 0

  the kinetic energy = 635.8 J

gravitation potential energy = U J

c. mgh = KE = 635.8
h = 2.6 m more then the uncopressed position.

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