Answer: (d)
Explanation:
Given
Mass of object 
Speed of object 
Mass of object at rest 
Suppose after collision, speed is v
conserving momentum

Initial kinetic energy

Final kinetic energy

So, it is clear there is decrease in kinetic energy . Thus, energy decreases and velocity becomes 2 m/s.
The correct answer is
C. reduce the friction between its moving parts
In fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.
Answer:
Energy is absorbed, so the mass is reduced.
Explanation:
The relationship between the mass and the energy is given by Einstein formula as :

m is the mass of an atom
c is the speed of light
When an atom is formed, the energy gets absorbed. As a result mass will decrease as per Einstein's equation. So, the correct option is (c) "Energy is absorbed, so the mass is reduced".