Question of the day

Radioactivity 

Q- Isotope 137 Cs of Cesium has a half life of 30 years. Suppose a distributor sells 5 grams of it in January 1, 2000. (a) Write an equation with giving the number of grams of the isotope left "t" years after January 1, 2000. (b) How many grams are present after 6 years?

Solution:

January 16,2026 05:47 PM - Comment(s)
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Average Density

Q- A cuboidal container with base area A is filled with water up to a height h. Small iron balls are dropped in the container till the upper layer of balls reaches the water surface. If the average density of the content in the container becomes ρ, what is the final height H of water level in t...

January 10,2026 10:22 AM - Comment(s)
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Mass added to an Oscillator

Q- A block with mass M attached to a horizontal spring with force constant k is moving with simple harmonic motion having amplitude A. At the instant when the block passes through its equilibrium position, a lump of putty with mass m is dropped vertically onto the block from a very small height and ...

January 07,2026 11:19 AM - Comment(s)
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Grid of Resistances

Q - An infinite square grid of resistances, each R is shown in diagram. If a battery of EMF V with negligible internal resistance is connected between points A and B, what is the current through the battery?

Solution:

December 27,2025 07:27 AM - Comment(s)
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Efficiency of an Engine

Efficiency of an Engine

Q- One mol of an ideal monatomic gas is used as the working substance in an engine. The engine operates on the cycle shown in the diagram. Processes BC and DA are reversible and adiabatic. What is the efficiency of the engine? 

Solution:

December 21,2025 10:28 PM - Comment(s)
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Particles on Triangles

Q- Three particles, located initially on the vertices of an equilateral triangle of side L, start moving with a constant tangential acceleration ’a’ towards each other in a cyclic manner, forming spiral loci that coverage at the centroid of the triangle. Find the length of one such spiral.

Solution:

December 17,2025 08:36 AM - Comment(s)
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Block falls on spring

Q- A small light disc is attached with one end of a spring of constant K, the other end is fixed to ground and stands vertical. a small block of mass m is dropped from a height h above the disc. Considering elastic impact and only vertical motion find the maximum velocity and maximum acceleration of...

December 08,2025 11:57 AM - Comment(s)
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Ray Optics: Refraction of light

The virtual depth of the fish in water.
November 23,2025 07:29 AM - Comment(s)
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Electrostatics: Capacitance

A spherical capacitor has two different layers of dielectrics between its plates. Their permittivity are ϵ1 for a < r < r0 and ϵ2 for r0 < r < b. Find the capacitance of this system by finding the total energy of the fields between the plates.

Solution:

October 29,2025 07:32 AM - Comment(s)
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Kinematics: Variable acceleration

Q- At t = 0, car A starts from rest at point 1. It moves with an acceleration of 0.4 t m/s^2. At the same time, car B starts from point 2, which is 225 m ahead, with a constant acceleration of 2 m/s^2 in the same direction. Find: 

(a) Speed of car A at the end of the 225 m section. 

(b)...

October 08,2025 11:19 PM - Comment(s)
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