Problems 23-25: A spring of stiffness, k, and un-stretched length, Lo is placed vertically on a horizontal surface. A block of mass M is initially held at rest pressing down on the top of the spring, such that the compressed length of the spring is L. The block is in contact with, but not attached to the spring, so when you release the block, the spring pushes it up all the way to the top of the top of the un-stretched length of the spring, at which point it is launched into the air. HIGHEST POINT REACHED BY BLOCK M BLOCK ON VERGE OF LEAVING SPRING o =? >hmax = ? RELAXED SPRING BLOCK HELD DOWN" SPRING COMPRESSED SPRING SPRING Lo M RELAXED RELAXED -.... 19 PHYS 172/172D EXAM 2 PRACTICE (200 Points) Spring 2022 Problem 23: [6 points] Three students present statements about how to find the speed v. at which the block is launched into the air at the top of the spring. Which is correct? Amy: You choose the block as the system and Earth and spring as the surroundings and your equation is: (MU; -0) =-Mg(L, - L) + =K,(L, - 1)2 Beth: You choose the block and spring as the system and Earth as the surroundings and your equation is : (MP3 - 0) + (0 -;ks(Lo - L)?) = -Mg(Lo - L) Cathy: You choose the block, spring, and Earth in the system, and nothing in the surroundings, then your equation is: (MOB -0) + Mg(Lo - L) = =ks(Lo - L)2 Amy is correct, but Beth and Cathy are wrong. Beth is correct, but Amy and Cathy are wrong Cathy is correct, but Amy and Beth are wrong. Both Amy and Beth are correct, Cathy is wrong. m None of them is correct