IIT-JEE Exam

A ball is dropped from a height of 20 m above the surface of water in a lake. The refractive index of water
is 4/3. A fish inside the lake, in the line of fall of the ball, is looking at the ball. At an instant, when the ball
is 12.8 m above the water surface, the fish sees the speed of ball as
(A) 9 m/s (B) 12 m/s
(C) 16 m/s (D) 21.33 m/s

Read Solution (Total 1)

The overall thing is the fish will perceive the ball to fall from a shorter height. So its speed at any time will also appear slower.
Its true V after (20 - 12.8) = 7.2m. will be sqrt. (2gh) = 12m/sec.
(12/4) x 3 = 9m/sec. observed by the fish.
10 years agoHelpfull: Yes(0) No(0)

IIT-JEE Other Question

Three concentric metallic spherical shells of radii R, 2R, 3R, are given charges Q1, Q2, Q3, respectively. It
is found that the surface charge densities on the outer surfaces of the shells are equal. Then, the ratio of the
charges given to the shells, Q1 : Q2 : Q3, is
(A) 1 : 2 : 3 (B) 1 : 3 : 5
(C) 1 : 4 : 9 (D) 1 : 8 : 18 Cv and Cp denote the molar specific heat capacities of a gas at constant volume and constant pressure,
respectively. Then
(A) Cp −Cv is larger for a diatomic ideal gas than for a monoatomic ideal gas.
(B) Cp + Cv is larger for a diatomic ideal gas than for a monoatomic ideal gas.
(C) Cp/Cv is larger for a diatomic ideal gas than for a monoatomic ideal gas.
(D) Cp. Cv is larger for a diatomic ideal gas than for a monoatomic ideal gas.