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A Physicist Driver confusing Police

A driver is stopped for running a red light. trying to avoid a ticket, the driver tells the police officer that because of the Doppler shift, the red light (650 nm) was blueshifted to a green light (470 nm). what would the drivers speed need to be for this to be true


Asked Sabnna

Would an underground nuclear explosion generate an Electromagnetic pulse?

Would an underground nuclear explosion generate an EMP? If so, how far would it be likely to travel?

Asked Daniel

You can get answer to your question here. If you need further clarification, please post as comment to this post.\



The indigenous Cryogenic Engine of India

The cryogenic engine used in indian rocket gslv is also called as?

Asked Shaaru

Answer: CE 7.5 was the first successful engine and CE-20 is the Cryogenic Engine developed by the Liquid Propulsion Systems Centre, a subsidiary unit of ISRO developed to power the upper stage of the Geosynchronous Satellite Launch Vehicle MK III  also referred to as the Launch Vehicle Mark 3 (LVM3).  It is the first Indian cryogenic engine to feature a gas-generator cycle   References ISRO website https://www.isro.gov.in/gslv-d5-gsat-14/indigenous-cryogenic-engine-and-stage    

Siphons and fluid dynamics

Working on a science fair project with my 3rd grader we got an unexpected result I am at a loss to explain.  We made a mock up toilet with two different drain pipes / siphons.  When we use the 3/4″ pipe we get a slow drainage that stops when the water in the bowl goes down to about the level of the crest of the siphon.  When we use the 1 1/2″ drain pipe we get a very strong flow and the water level drops all the way down until air can enter the siphon, so the water level drops way below the top of the siphon, down to the intake opening.  I understand that more water travels though the larger pipe, hence the faster flow rate, but I can’t explain the difference in the ending water level in the bowl.  What forces are at work here?  How can we further test or prove these principals?


Asked Dan

Why do we take differential element “dx” from the origin at a distance “x” only?

Why do we take differential element “dx” from the origin at a distance “x” only.(the variable “x” and x in “dx” are same.why?)


Asked Suraj

What s the initial Horizontal Velocity of the Bomb?

An aircraft is flying along a horizontal path with a velocity 30 m per second at 625m above the ground level. A bomb is released at rest with respect to the plane. At the same time, a cannon yard which is on the ground right below the aircraft ,fires a bullet at angle of 45 degrees to the horizontal as it strikes the bomb. What is the initial horizonatal component of velocity of the bomb?


Asked Nishali

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November 2018

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