The best statement would be number 3. Sound waves move perpendicular to the medium particles.
The question in choice-C is the correct answer to your question.
(Is this confusing ?)
Answer:
34.6 m/s
Explanation:
From conservation of momentum, the sum of initial and final momentum are equal. Momentum is a product of mass and velocity. Initial mass will be 42.8+31.5+25.9=100.2 kg
Final mass will be 31.5+25.9=57.4 kg
From formula of momentum
M1v1=m2v2
Making v2 the subject of the formula then

Substitute 100.2 kg for M1, 19.8 m/s fkr v1 and 57.4 kg for m2 then

Acceleration = (change in speed)/(time for the change)
Change in speed = (end speed) - (start speed)
Change in speed = (10 m/s) - (20 m/s) = -10 m/s
Time for the change = 5.00 seconds
Acceleration = (-10 m/s) / (5 sec)
<em>Acceleration = -2 m/s²</em>
That's choice-A .