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Devna asked.

find the potential at A ….a prson brings a mass of 1 kg from infinity to the pt A .initially the mass was at rest but it moves at a speed of 2 m/sas it reches A .the work done by person on mass is -3 J

Is it true that a person touching a high power line get struck with the line?

Amritha Asked:

Is it true that a person touching a high power line get struck with the line?


Ya, This is due to the strong contraction of the muscles making the person not at all able to release the wire or object from which he got the shock. Not due to any type of attraction arising out of electricity.

How wheel + Tyre diameter affects a vehicle’s speed

I have been told a larger wheel/tyre decrease acceleration because its harder to turn the wheel making the car rev slower.

But the same person tells me it will increase the top speed.

My question is if the car has a max rev of 8000rpm but only reaches 7000rpm in its highest gear would a smaller wheel/tyre not make it easier for the car to rev higher thus possible increasing the top speed by using a smaller wheel?

(Garry asked)

As wheel radius increases, its top speed increases for a given RPM since for a given RPM the speed of the vehicle is directly proportional to its radius.
The distance traveled in one rotation = 2 π R
But now, there is another effect also here. As the radius of tyre increases, its moment of inertia increases and it would be harder for the engine to rotate it. So, the engine will not be able to turn it with the same ease as before, but however, there will be an increase in top speed other conditions remaining the same.
Monster Truck
Refer to http://wahiduddin.net/calc/calc_speed_rpm.htm for a calculation of top speed vs tyre radius

Time Travel

Abhirami asks:

Suppose there are two brothers who are twins. One of them travels in space by orbiting earth  at a very high speed for a few years, and the other one stays on earth.When the person who had travelled in space comes back to earth, he would be looking much younger than his twin brother. Why is it so?

Relative velocity in free fall

If a person jumps out of a plane, and a few seconds later, another person jumps, why is it that the difference in their velocities stays the same? Shouldn’t it decrease because eventually, the first diver will reach maximum velocity, but the other diver will be slower at first, but then he reaches max. velocity as well…I’m not wording it the best way, but any help would be greatly appreciated :]

[Posted by Iris]

Both are examples for free fall. The velocity at any instant is given by v = gt

If for the first one, time = t and for the second who jumps after n seconds, time=t-n

Therefore, velocity of the first one at any instant, v1=gt

for second one, v2=g(t-n)

The difference in velocities,

v1-v2 = gn, which shows that the difference in velocity remains constant.

This is because, both are moving with the same acceleration and their velocities are increasing at the same rate

Path of an object

If a man tossed a coin in a moving train and the coin fell back . Then in which type of motion train is moving? and how?



For the person who tosses the coin the motion is vertically upward if he do so. But for an observer outside the train the path of the stone is a parabola.This is due to the horizontal velocity of the stone.

If the stone fell back, it means that the train is accelerated. If it were moving with a constant velocity, then the stone would’ve reached back to his hands only as both the train and the stone possess the same horizontal velocity.

Why the shock of alternating current is attractive ?

Why the shock of    alternating current  is   attractive ?


Shock is never attractive. I have experienced shock from AC several times, but never felt any attraction. But, during a severe shock it seems that the person  is attracted by the electricity due to the fact that the electricity temporarily disables his nervous system and the muscles get contracted and he cannot move nor even throw away the device causing shock. But this is not due to attraction

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January 2021

Schrodinger’s Cat in Daily Life

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