If you notice that two waves combine and a part of the resulting wave has less light intensity than either of the individual waves, you're observing a. destructive interference. b. polarization. c. constructive interference. d. diffraction.

The correct option is A.
Destructive interference is said to occur when two waves of equal frequencies and opposite phase merge in such a way that the negative displacement of one wave coincides with the positive displacement of the other thus cancelling each other out.

a)

m

b)

ms⁻¹

Explanation:

= mass of the wood block = 2 kg

= initial speed of the block at the bottom = 13 m/s

= angle of incline = 27°

= Coefficient of kinetic friction = 0.2

= kinetic frictional force

= height of the incline gained

= length of the incline traveled

In triangle ABC

= Normal force on the block by incline surface

From the force diagram of the block, force equation perpendicular to the incline surface is given as

                           Eq-1

kinetic frictional force on the block is given as

Using Eq-1

Work done by kinetic frictional force is given as

Using conservation of energy

Kinetic energy at the bottom = work done by frictional force + potential energy at the top

inserting the values

m

b)

= final speed of the block after returning to starting point

Using conservation of energy

Kinetic energy at the bottom initially = work done by frictional force + Kinetic energy at the bottom finally

inserting the values

ms⁻¹