18. A system consists of three billiard balls. Each ball has mass m and is trave

Question

18.

A system consists of three billiard balls. Each ball has mass m and is traveling at speed v. One ball is traveling north, another ball is traveling east, and the third ball is traveling south. What is the momentum of the system?

mv, heading west

mv, heading east

mv, heading east   <- (or Square Root of 2 mv,heading east)

3mv, heading east

19.

A 0.24-kg blob of clay strikes a wall with an initial velocity of 25m/s. The clay comes to a stop against the wall in 91ms What is the average impact force on the clay?

66 N

41 N

80 N

55 N

20.

A block of mass m = 4.4 kg slides from left to right across a frictionless surface with a speed Vi=8.4m/s. It collides in a perfectly elastic collision with a block of mass M that is at rest. After the collision, the 4.4-kg block reverses direction, and its new speed is Vf=2.5 m/s What is M?

6.8 kg

7.4 kg

8.8 kg

8.1 kg

18.

A system consists of three billiard balls. Each ball has mass m and is traveling at speed v. One ball is traveling north, another ball is traveling east, and the third ball is traveling south. What is the momentum of the system?

mv, heading west

mv, heading east

mv, heading east   <- (or Square Root of 2 mv,heading east)

3mv, heading east

Explanation / Answer

(18) Momentum of ball traveling in south and north nullifies

Hence momentum of system is mv ,heading east

(19) Impact force = m dv /dt = 0.24 * (25/0.091) = 65.94 kg = 66 kg

(20) Momentum conservation

m u1 + M u2 = m v1 + M v2

4.4 * 8.4 + 0 = - 4.4 * 2.5 + M* v2

M v2 = 47.96 kg m/s

Conservation of energy

0.5 m u1^2 = 0.5 mv1^2 + 0.5 M v2^2

0.5 * 4.4 * 8.4^2 - 0.5 * 8.4 * 2.5^2 = 0.5 M v2^2

M v2^2 = 337.964 J

M = (M v2)^2 / M v2^2 = 47.96^2 / 337.964 = 6.8 kg

M = 6.8 kg

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