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A 10 kg ball travelling at 10*sqrt(3) m/s along the +X-axis strikes a stationary 20 kg ball. After impact the 10 kg ball stops, and the 20 kg ball breaks into two equal 10 kg fragments. One fragment moves along the +Y-axis at 10 m/s; the other moves at 20 m/s making an angle theta with the X-axis. Find theta (in degrees, nearest integer).

1. 30
2. 45
3. 60
4. 90

Correct answer: 30

Solution

Y-momentum: 10*10 (up) + 10*20*sin(theta with -y) must be zero, and X-momentum equals the initial momentum; solving gives theta = 30 deg below the X-axis.

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