Here in all such collision type question we can use momentum conservation as we can see that there is no external force on this system

as we know that




now from above equation we have



so the speed of combined system is 2 m/s
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Answer:
A-the energy of the wave decreases gradually
Explanation:
when a wave is acted upon by an external damping force the energy of the wave decreases gradually.
The energy degrades into the form of heat which is considered to be of less value and use. The reason is because it disperses and spreads more widely.
So therefore it end up as heat with a little sound but that is close to none because that too disperses into heat i.e. decreased form of energy.