The answer is diffraction or interference
Power is the work performed divided by time in seconds. The work is the force times distance:

the time in seconds is 60*11+30=690s so the power is

So choice B
Answer:
5/6 = 0.833
Explanation:
From conservation of momentum,
m1*u1 + m2*u2 = (m1+m2)*v
v = (m1*u1 + m2*u2)/(m1*m2)
Putting in the values, we get, v = 5/6 = 0.833