a glider of mass 0.150 moves on a horizontal frictionless air track. it is permanently attached to one end of a massless horizontal spring, which has a force constant of 10.0 both for extension and for compression. the other end of the spring is fixed. the glider is moved to compress the spring by 0.180 and then released from rest. calculate the speed of the glider (a) at the point where it has moved 0.180 from its starting point, so that the spring is momentarily exerting no force and (b) at the point where it has moved 0.250 from its starting point.