(c) An ice hockey puck of mass m travels with constant speed u in a straight lin

Question

(c) An ice hockey puck of mass m travels with constant speed u in a straight line on the surface
of an ice rink. Let its direction of motion define the x axis. The puck collides with another
puck of the same mass that is at rest. The first puck emerges from the collision, with a speed
v1 at an angle of 30 with respect to the x axis. The second emerged at speed v2, at an angle
of -45 relative to the x axis.
(i) Sketch a diagram to show how this collision proceeds. [1 mark]
(ii) Work out the ratio, v1=v2. [2 marks]
(iii) Obtain an expression for v1 in terms of u. [3 marks]
(d) If u is 30 m s??1, what are the values of v1 and v2. What fraction of the initial kinetic energy
is lost in the collision? [4 marks]
(e) Explain how you could know, before beginning any calculations, whether this collision was
elastic or inelastic? [2 marks]

Explanation / Answer

We need to conserve linear momentum along x-axis... and along y-direction, the velocities should be equal and opposite..
So...
b.)Along y-direction:
V1sin30= V2sin45
v1=v2 v2

Along x-axis: momentum conservation----
v1cos30+v2cos45=u


c.)v1(1+v3)=2u
v1=2u/(1+v3)

d.)intial KE= 450m
v1= 21.96
v2=15.5
final KE= 361.24m
so energy lost= 88.75m
fraction= 71/360

e.) inelastic collision. as energy is lost in collision

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