Two mirrors X and Y are shown to be inclined to each other at 100°. A ray of light falls
upon mirror X as shown. The angle of incidence upon mirror Y is
a) 15 degrees
b) 30 degrees
c) 40 degrees
d) 100 degrees

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.

not too sure thinking all accelerations are pointed down