In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest.
Answer:E
Explanation:
It is given that Energy of gamma ray is E=1.2 Mev
Shielding effect can be measured by measuring the fraction of gamma rays blocked by shield. If certain thickness will able to block half the radiation then to block 75% radiation we need to add same amount of thickness in order to block the remaining radiation.
i.e.
fraction is blocked by 10 cm thickness
then remaining radiation is 
another 10 cm thickness will block the remaining half radiation i.e.
so total 75 % radiation will be blocked
Initial velocity =0, a=3m/s2, final velocity =18m/s, 18=3t, t=6 sec
Interference if the hardest to remove due to the superposition of the frequencies of the radio waves