Rishi's Physics Thread

[Yacoubb]

Thanks so much zealous'

 how would you do the following question

I have worked out the initial speed to be 20m/s and the maximum height to be 20m

how would you find the speed of the cork as it returned to its
starting point?

What is the answer? I've done some working out, but I'd like to make sure I'm correct before I submit an explanation

[knightrider]

What is the answer? I've done some working out, but I'd like to make sure I'm correct before I submit an explanation

the answer says 20m/s

[Yacoubb]

the answer says 20m/s

Yeah, I got that too.

Okay, so first of all, let's begin with some of the data we have. We know that the total time it takes for the cork to travel up and down is 4.0s; we can now assume that the time taken for the cork to travel from it's maximum height of 20m to the ground is 2.0s.

At the maximum height, we can assume that the value of the velocity is 0 m/s. This is because at the maximum height, we assume that the cork has reached a point of temporary rest.

u = 0m/s
a = 10m/s
v = ?
t = 2s

v = u + at
v = 0 + 10*2
v = 20m/s

[Rishi97]

In regards to the photoelectric effect:
Explain why the maximum kinetic energy of electrons ejected by light of a higher frequency is greater than the maximum kinetic energy of electrons ejected by light of a lower frequency

Urgent replies appreciated

[Zealous]

In regards to the photoelectric effect:
Explain why the maximum kinetic energy of electrons ejected by light of a higher frequency is greater than the maximum kinetic energy of electrons ejected by light of a lower frequency

Have a look at the formula for the kinetic energy (max) of an electron:
where W is the work function of the metal.

The higher the frequency of incoming light, the greater energy the photon has. For electrons to be emitted, the energy of the incoming photon must first be greater than the work function. Any extra energy on top of the work function will go into the emitted electron. So the higher the frequency of incoming light, the greater the kinetic energy of an emitted electron from the metal.

Bit hard to explain this stuff, hopefully it helps a bit!

[Rishi97]

Calculate the de Broglie wavelength for a neutron with kinetic energy 3.00 x 10^-18 J
info:
mass of neutron= 1.67 x 10^-27 kg

[Zealous]

Calculate the de Broglie wavelength for a neutron with kinetic energy 3.00 x 10^-18 J
info:
mass of neutron= 1.67 x 10^-27 kg

de Broglie's wavelengh: where h=Planck's Constant and p=momentum of the matter.

How do we find the velocity? Use the formula for the kinetic energy:



Now substitute the value for 'v' into de Broglie's wavelength equation:



This formula isn't on the formula sheet, so it might be worth taking note of this. 

Now all you have to do is substitute h (in Joules! Important!), m and Ek.

[Rishi97]

de Broglie's wavelengh: where h=Planck's Constant and p=momentum of the matter.

How do we find the velocity? Use the formula for the kinetic energy:



Now substitute the value for 'v' into de Broglie's wavelength equation:



This formula isn't on the formula sheet, so it might be worth taking note of this. 

Now all you have to do is substitute h (in Joules! Important!), m and Ek.

ooo thanks
But when u subbed in v into the de Broglie equation, how did the m become rooted and squared? Not the best at maths so sorry for the noob question
Thanks Zealous

[JHardwickVCE]

ooo thanks
But when u subbed in v into the de Broglie equation, how did the m become rooted and squared? Not the best at maths so sorry for the noob question
Thanks Zealous

As squaring and square rooting are inverse operations, we can deduce

When functions are under a square root and multiplied, we can combine them underneath one single square root

[JHardwickVCE]

Apologies, that should be a square root sign.

Moderator Action: fixed it up for you JHardwickVCE =) You can use \sqrt{} for the square root sign.

[Rishi97]

In regards to structures and materials:
Is strain energy per unit volume the same as toughness?

[S61778]

Hey

Could someone please tell me how the existence of standing waves support the fact that an atom has discrete energy levels.

Thanks