The 14-in. spring is compressed to an 8-in. length, where it is released from rest and a...

The 14-in. spring is compressed to an 8-in. length, where it is released from rest and accelerates block A. The acceleration has an initial value of 400 ft/sec² and then decreases linearly with the x-movement of the block, reaching zero when the spring regains its original 14-in. length. Calculate the time t for the block to go (a) 3 in. and (b) 6 in.