Question

Two hockey pucks approach each other as shown in the figure below. Puck 1 has an initial speed of 19 m/s, and puck 2 has an initial speed of 14 m/s. They collide and some glue on one of the pucks causes them to stick together. (Assume the pucks have the same mass.) (a) If the two pucks form a ''system'' is the momentum of this system along x or y conserved? (b) Find the components along x and y of the initial velocities of both pucks. (c) Express the conservation of momentum condition for motion along x and y. (Let v1ix and v1iy be the x and y components of the initial velocity for puck 1, v2ix and v2iy be the x and y components of the initial velocity for puck 2, and vfx and vfy the x and y components for the final velocity.) (d) Is this collision elastic or inelastic? (e) Find the final velocity of the two pucks after the collision. (f) What fraction of the initial kinetic energy is lost in the collision?

Answer 1

a)
yes
b)
puck 1 x component = 19 * cos 30 = 16.45 m/s
puck 1 y component = -19 * sin 30 = -9.5 m/s
puck 2 x component = 0 m/s
puck 2 y component = 14 m/s

c)
V1ix+V2ix = 16.45 + 0 = 16.45 m/s
V1iy+V2iy = -9.5 + 14= 4.5 m/s

d)
inelstic collision

Since they stick together

e)
use conservation of momentum in x direction
m*V1ix+m*V2ix = (m+m)*Vfx
m*V1ix+m*V2ix = 2m*Vfx
V1ix+V2ix = 2*Vfx
16.45 = 2*Vfx
Vfx = 8.225 m/s

use conservation of momentum in x direction
m*V1iy+m*V2iy = (m+m)*Vfy
m*V1iy+m*V2iy = 2m*Vfy
V1iy+V2iy = 2*Vfy
4.5 = 2*Vfy
Vfy = 2.25 m/s

magnitude= sqrt (Vfx^2 + Vfy^2) = sqrt (8.225^2 + 2.25^2) = 8.53 m/s
direction = atan (vfy/vfx) = atan (2.25/8.225) = 15.3 degree

Only 4 parts at a time please