The initial momentum of the system can be expressed as,

The final momentum of the system can be given as,

According to conservation of momentum,

Plug in the known expressions,

Initially, the second mass move towards the first mass therefore the initial speed of second mass will be taken as negative and the recoil velocity of first mass is also taken as negative.
Plug in the known values,

Thus, the final velocity of second mass is 2.99 m/s.
Answer:
Option B, Some of the cars' kinetic energy was converted to sound and heat energy.
Explanation:
In an elastic collision, no energy is lost during and after collision. Thus, it can be said that in an elastic collision both momentum and kinetic energy remains conserved.
While in non-elastic collision, kinetic energy of the system is lost. However, the momentum of the system is conserved. Generally, during and after collision some of the kinetic energy is lost as thermal energy, sound energy etc.
Hence, option B is correct
Answer:
The amplitude of vibration of string will increase due to which loudness of sound will increase
Explanation:
As we know that the guitar is based on the principle of Resonance. When string of the guitar vibrates at a given frequency then the sound produced in the hollow part of the guitar will also be at same frequency.
This is known as resonance condition, so guitar will produce same frequency sound as that of frequency of string.
Now if the string is plucked with increasing level of force then it will increase the amplitude of vibrations of the string due to which the sound produced in the guitar will also be of same level.
So here we can say that amplitude and intensity of sound related as

so on increasing amplitude the intensity will increase and hence it will produce loud sound