In a pool game, a ball of mass in = 50g is hit by u billiard cue, acquiring n sp

Question

In a pool game, a ball of mass in = 50g is hit by u billiard cue, acquiring n speed v, = 50m/s. It successively strikes another ball, of the same mass m and initially at rest. Assuming that the motion of the particles is confined on one dimension only, the final velocity of the first ball after the knock is v if = 48m/s, while the final velocity of the second ball is v2 = 2m/s. Show that the linear momentum is conserved during the process, while the kinetic energy is not. Explain why the kinetic energy is not conserved. How much kinetic energy has boon lost?

Explanation / Answer

a) initial momentum = mv1i = 50 m

final momentum = mv1f + mv2f = 48 m + 2 m = 50 m = initial momnetum,

so momentum is conserved.

b) initial kinetic energy = mv1i2/2 = 50*10-3 * 502/2 = 62.5 J

final kinetic energy = mv1f2/2 + mv2f2/2 = 50*10-3 * 482/2 + 50*10-3 * 22/2 = 57.7 J initial kinetic energy

because some non-conservative force did work.

kinetic energy lost = 62.5 - 57.7 = 4.8 J

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