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Speed of Light and Protons

If the definition of the speed of light is for massless particles, then how is a proton, having mass, accelerated to the speed of light?  This sounds like a conumdrum.

Posted Thierence


No massive particle has not so far crossed the speed of light. Even the extremely light particles – the neutrinos – couldnot cross the speed of light. Protons have not crossed the speed of light. When it nears the speed of light, the relativistic mechanics will become prominent and the it is to be treated is different from the classical mechanics.

Force – Impulse – Momentum

Hi All! I’m having mega problems with one part of a physics assignment. Looking for any help.
The details are as follows:

The diagram shows the normal force on Christine’s feet vs. time, as recorded by a force plate while she stands still initially (until point B), then jumps off the plate. (This trial is separate from the one in the previous problem. The graph is over-simplified and idealised, compared to reality.) When her feet leave the plate, the normal force is zero.

1)What is the magnitude of the (upward) impulse generated by the normal force of Christine during the time interval of her jump off the plate?

2)What is the magnitude of the downward impulse due to gravity during this interval?

3)What is the net impulse which propels her upwards when she jumps off the plate? (Recall, the net force on her is the normal force minus the force of gravity.)

4)What is her change in speed upwards for this process?

The graph has NORMAL FORCE (N) on the y-axis and TIME (s) on the X axis.
The line is at a constant 550 N until point B (1.75 seconds) at which time it shoot up vertically to 1550 N at a time of 1.95 seconds. It peaks at this time and position then drops down to 0 N at 2.15 seconds.

Thanks in advance for any guidance that can be provided!


Conservation of linear momentum – Problem

Astronauts Mr.X and Mr.Y float in a zero gravity space with no relative velocity to one another. Mr. Y throws a mass of 5 kg towards X with speed 2 m/s. If Mr. X catches it, the change in velocity of X and Y are (choose the correct option)
(a) 0.21 m/s, 0.80 m/s
(b) 0.80 m/s, 0.21m/s
(c) 0.12 m/s, 0.08 m/s
(d) 0.08 m/s, 0.12 m/s

Please provide me the solution part step by step

Escaping from gravity

Hello everyone,

Plot of a two-dimensional slice of the gravita...

ever since I heard of the concept of a gravity well I’ve had a great deal of trouble coming to terms with the fact that gravity’s actual pull in infinite ( though admittedly very small at large distances due to the inverse square law ). Is there any way someone could explain to me how it is possible to escape the effects of something with infinite range?


Asked Elias Tragas

Newton’s Third Law of Motion and some doubts

Newton’s Third Law of Motion states that

“Every action has equal and opposite reaction”

In other words,

“Whenever a body exerts a force on another body, the second body exerts an equal and opposite force on the first body”

 Osho Garg asks:

“if a person is sitting on a chair both the chair and person exert force against it so we called that ” there is always an equal and opposite reaction ” but for example a elephant of mass 584 kg sit on a chair, the chair will broke.  So what we called for this . Please explain.



When an elephant “sits” on a chair, it breaks because it cannot give the “equal reaction” and  it “yields” to it.

Therefore, here the force is doing “work”.

More discussions are welcome

Particle and Field

Is it necessary that particles should be present for the presence of a any field ?for example in higgs field,  higgs boson are the particles which are responsible for it.

Asked Sandeep

Speed of Gravity

Why hasn’t anyone measured the speed of gravity yet?

As in, how long does it take for the gravitational field of a mass to affect another mass?

Musaddiq Sajjad asked.


Gravitational Lensing in Galaxy Cluster Abell 37

Who said that speed of gravity waves is not measured?

Please go through the links below and you ca get details,

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April 2021

Schrodinger’s Cat in Daily Life

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