A Bludger is a iron ball used in the game quidditch. It is 10 inches in diameter

Question

A Bludger is a iron ball used in the game quidditch. It is 10 inches in diameter and has a mass of 68.0 kg. Players, called beaters, try to hit these balls at opposing players. A player named Draco (mass = 64.0 kg) was travelling to the left at 6.375 m/s, when he is struck by a bludger traveling to the right at 6.00 m/s. Draco and the ball stick together after the collision.

a) What is the total kinetic energy prior to the collision?

b) What is the total momentum before the collision?

c) What is their speed after the collision?

d) What is the kinetic energy after the collision?

e) What is the total momentum after the collision?

Explanation / Answer

a)

consider left as negative direction and right as positive

mb = mass of ball = 68 kg

vb = speed of ball = 6 m/s

md = mass of draco = 64 kg

vd = speed of drago = 6.375 m/s

Total Kinetic energy prior to collision is given as

TKE = (0.5) mb vb2 + (0.5) md vd2 = (0.5) (68) (6)2 + (0.5) (64) (6.375)2

TKE = 2524.5 J

b)

Total momentum before collision is given as

Pi = mb vb + md vd = (68) (6) + (64) (- 6.375)

Pi = 0 kgm/s

c)

V = final speed after collision

using conservation of momentum

Pi = (mb + md) V

0 = (68 + 64) V

V = 0

d)

hence final KE = 0

e)

Pf = Pi = 0

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