Exam 2 Item 10 Constants Part A A ball of mass 0.275 kg that is moving with a sp

Question

Exam 2 Item 10 Constants Part A A ball of mass 0.275 kg that is moving with a speed of 5.6 m/s collides head-on and elastically with another ball initially at rest. Immediately after the collision, the incoming ball bounces backward with a speed of 3.6 m/s Calculate the velocity of the target ball after the collision. Express your answer to two significant figures and include the appropriate units. Value Units Submit Part B Calculate the mass of the target ball Express your answer to two significant figures and include the appropriate units. e

Explanation / Answer

Conservation of momentum

before = after

m1 v1 + m2 v2 = m1 u1 + m2 u2

(0.275) (5.6) + m2 0 = (0.275) (-3.6) + m2 u2

1.54 = -0.99 + m2 u2

2.53 = m2 u2 ----------------(1)

Kinetic energy is also conserved

1/2 (m1 v1^2 + m2 v2^2) = 1/2 (m1 u1^2 + m2 u2^2)

(0.275) (5.6)^2 + 0 = 0.275 (-3.6)^2 + m2 u2^2

8.624 – 3.564 = m2 u2^2

5.06 = m2 u2^2 -------------------(2)

use (1) u2 = 2.53/m2

5.06 = m2 (2.53/m2)^2

5.06 = 6.4/m2 ---> m2 = 1.26 kg = 1.3kg (ans of part B)

From eqn (1):

u2 = 2.53/m2 = 2.53/1.26 = 2.0 m/s (ans of part A)

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