JEE Main/Advanced Courses Online
Why are Ships Red Below the Waterline
Q: Why are most ships painted red below the waterline?
A: Ships are primarily painted below the waterline with anti-fouling paint to prevent marine growth. This paint traditionally contains cuprous oxide, which creates a natural red tint; the colour is a functional byproduct of the protection rather than a stylistic choice.
Permutations ~ Crocodile Problem
A crocodile is known to have not more than 68 teeth. Find the total number of crocodiles with different set of teeth ignoring any variations in teeth themselves.
There are 68 slots and in each slot the tooth can either be present or absent. So, there are 2 ways for each slot. 2 is multiplied 68 times giving answer as 268.
Going Uphill – How?
You have a V-shaped track that is slightly inclined. When a cylinder is placed at the lower end of the track, it stays put or rolls further down. However, when a double cone (two cones joined at their bases) is placed at the lower, narrow end of the track, it appears to spontaneously roll upward toward the higher, wider end.
What may appear as magic at first thought is actually not magic as while it looks like the double cone is moving up, its center of mass is actually moving downward. The rails of the track are not parallel; they diverge (spread apart) as they go “up” the incline. As the double cone rolls toward the wider end of the track, the points of contact between the cone and the rails move outward toward the thinner part of the cone. Because the cone is thicker in the middle than at the tips, the central axis (where the center of mass is located) actually gets closer to the ground as the rails spread apart. So, the cone’s center of mass falls due to the diverging tracks.
Atomic Electrons Quiz
Among the following, the correct statement(s) for electrons in an atom is(are)
(A) Uncertainty principle rules out the existence of definite paths for electrons.
(B) The energy of an electron in 2s orbital of an atom is lower than the energy of an electron that is infinitely far away from the nucleus.
(C) According to Bohr’s model, the most negative energy value for an electron is given by n = 1, which corresponds to the most stable orbit.
(D) According to Bohr’s model, the speed of electrons increases with increase in values of n.
Will Planes Cross?
Plane A flies at a constant speed of 300 km/h. Plane B is 225 km behind plane A and flies at an initial speed of 420 km/h, but due to fuel limitations, its speed decreases linearly by 30 km/h every hour. Assume both planes fly in horizontal path at safe distance from each other.
(A) They will cross each other at t = 3 hrs. only
(B) They will cross each other at t = 5 hrs. only
(C) They will cross each other two times
(D) They will never cross each other
Plane on Runway
Consider an aeroplane covering the entire runway 3.5 km long before take-off. The initial speed of the plane is zero and the final speed just before take-off is 174 knots (1 knot = 1.852 kmph). Assuming the acceleration to be constant, how much time is taken to cover the runway?
Man-Made Vs God-Made
An astronaut sitting in a chair in a satellite feels weightless. However, Moon is also a satellite and the astronaut does not feel weightless there. Are laws of Physics different for man-made satellite and the God made satellite?