In: Physics
Problem 2 A block of mass 1 kg is sitting on top of a compressed spring of spring constant k = 300 N/m and equilibrium length 20 cm. Initially the spring is compressed 10 cm, and the block is held in place by someone pushing down on it with his hand. At t = 0, the hand is removed (this involves no work), the spring expands and the block flies upwards.
(a)Draw a free-body diagram for the block while the hand is still pressing down. Try to get the forces approximately to scale. The following question should help.
(b)What must be the force (magnitude and direction) exerted by the hand on the block?
(c)How much elastic potential energy was stored in the spring initially?
(d)Taking the system formed by the block and the earth, how much total work is done on it by the spring, as it expands to its equilibrium length? (You do not need to do a new calculation here, just think of conservation of energy.)
(e)How high does the block rise above its initial position?
(f)Treating the block alone as the system, how much net work is done on it by the two external forces (the spring and gravity) from the time just before it starts moving to the time it reaches its maximum height? (Again, no calculation is necessary if you can justify your answer.)