A boy stands at the base of a building and throws a rock vertically upward (+y direction) with an initial speed of v0 = 24.0 m/s. How long after the rock is initially thrown will a person 15.0 m above him see the rock for the first time?

The great sandini is a 60.0-kg circus performer who is shot from a cannon (actually a spring gun). you don’t find many men of his caliber, so you him design a new gun. this new gun has a very large spring with a very small mass and a force constant of 1100 n/m that he will compress with a force of 4400 n. the inside of the gun barrel is coated with teflon, so the average friction force will be only 40.0 n during the 4.00 m he moves in the barrel. at what speed will he emerge from the end of the barrel, 2.50 m above his initial rest position?