FOUR USES OF CONCAVE MIRROR:Satellite dishes,headlights of a car, telescopes used for astronomical studies, and shaving mirrors because of there curved and reflective surface.
FIVE USES OF LENSES: Camera lens ,microscopes ,magnifying glass,eyeglasses,projector
Answer: a) 0.78 m/s b) 1.57 m/s
Explanation:
M = father's mass
m = son's mass = M/3
V = father's initial speed
v = son's initial speed
(1/2)MV^2 = (1/2)*(1/2)*m v^2
M*V^2 = (1/2)(M/3)v^2
V^2/v^2 = 1/4
V = v/2
Second equation:
(1/2)M*(V + 1.4)^2 = (1/2)m*v^2
= (1/2)*(M/3)*(3V)^2
cancel out the M's and (1/2)'s
(V + 1.4)^2 = 3V^2
V^2 + 2.8V + 1.96 = 3V^2
V^2 -1.4V -0.98 = 0
V^2 = 0.98/0.4 = 2.45
V = 1.57
To solve this problem we will apply the concepts related to Reyleigh's criteria. Here the resolution of the eye is defined as 1.22 times the wavelength over the diameter of the eye. Mathematically this is,
Here,
D is diameter of the eye
The angle that relates the distance between the lights and the distance to the lamp is given by,
For small angle, 
Here,
d = Distance between lights
L = Distance from eye to lamp
For small angle 
Therefore,
Therefore the distance is 5.367km.
The answer is D, because the collision's between molecules are elastic, not inelastic.
