Question

C. Now calculate your velocity and kinetic energy just before you hit the wall. (5pts) (if you couldn't do the previous problem, say that the momentum of you + the wall was 210 kg*m/s) d. A bit later in the evening, you go back for a second try... Running forward at a velocity of 9.00m/s, you don't notice that someone has removed the padding from the wall! Luckily, you are wearing a helmet, and you collide head-first with the wall, bounce off, and stop dead in your tracks. What will be the velocity of the wall moving forward? (5pts) e. Was this collision in part d. elastic or inelastic? How much energy has your helmet absorbed (and saved your brain from) in this collision ? (5pts)

Answer 1

The gravitational potential energy is given by: a. U %3D (т, + m2)gh U = (62.5 + 123)(9.8)(0.950) U = 1727 J b. Using the conservation of energy, the initial kinetic energy must be equal to the gravitational potential energy: K = U K = 1727 J - (т, + т)0? %3D (т, + т.)gh Then: v = /2gh v = V2 * 9.8 * 0.950 т v = 4.32 - The momentum of the system after the collision: т p = (m, + m2)v = (62.5 + 123) * 4.32 = 801.36 kg- Using the conservation of linear momentum: C. Po = PF m,vo = 801.36 62.5 * vo = 801.36 т Vo = 12.8- d. Using the conservation of momentum: тv, 3D му 62.5 * 9 = 123 * V т V = 0.508