a small sphere of mass 3 kg that is hanging under a string is pulled to an initial height of 1.7 m and released from rest. it swings down and hits a block of mass 7 kg, then bounces back to the same side to a height of 0.5 m. the block was initially sitting on a platform that is at a height 0.7 m above the ground. find the velocity of the block in m/s immediately after it was hit by the sphere. use g