Two cars are driving 36 km/h and are coming from opposite directions.

(like this: car 10m/s --> <-- car 10 m/s)

They each weigh 1000 kg. Then they crash. What is the relative speed and energy of this crash?

My thoughts:

I think most people will say the relative speed of the crash is 20 m/s, and therefore the energy in the crash is according to E=0.5*m*v^2,

= 0,5*1000*20^2 = 200000

But if you calculate the energy that each car individually has, it's only E = 0,5*1000*10^2, = 50000. So with two cars the total energy can only be 100000? ]]>

(1=1. When we put 2 into equation, 1:2=1:2. It means it is changed 1=1 into 2=2. This means number is changed.) It is black hole. So physics formula as v=at(speed) means true as basic from its origin. (E=m*c^2) ]]>

can I say:we know only facts about how atoms do react after or during a disturbance? We do not know what an undisturbed atom is!? The properties of an undisturbed atom are in general unknown.

Can I conclude: an undisturbed atom can be something completely different compared to how we understand it in science.

Thank you in advance

Lothar ]]>

without friction over the ground, but the interface between the masses is rough, μ=0.5.

Determine the accelerations of the masses if the force P in the cable is: (i) 60 N, (ii) 40 N

https://imgur.com/a/GmZXZ

I drew the FBD for mass A and got this:

y: -W + N = 0 => N=W=196.2

x: 2P - Fri = ma = 20a

And from both equations I got a=1.096 m/s^2 , which is correct

But I can't seem to find the acceleration for the second mass.

Would the force acting on mass B be the same as the friction force on A (but in opposite direction), since that is the force that will be moving the object? For the FBD, the weight of A would be acting downwards, as well as the weight of B. What are the reaction forces gonna be? I am really confused on how the two objects will interact since I've never done similar dynamics problems before.

Thanks for anyone who helps ]]>

I'm having trouble trying to mathematically model a dynamic system. I tried to draw the system up and write out the algebraic governing equations in the attachment. In short, a compressed spring is pushing on a syringe plunger, which is pushing a liquid through a small radius tube. I want create a dynamic system model, but I'm kind of stuck! Any help would be appreciated!

Thanks!

J

Two charges, q1 = −3.00 mC and q2 = 4.50 mC, are located at −2.00 cm and 3.00 cm on the x axis, respectively. What are the magnitude and direction of the resulting field at (a) x = −3.00 cm? (b) x = 0 cm? (c) x = 5.00 cm?

My physics book doesn't bother explaining how to work field problems so I'm not sure what I'm doing wrong. I've been struggling with charge direction in electric and magnetic fields so I suppose I don't have a very good understanding of that. Anyway, in my latest attempt to solve this problem I used Coulomb's law to find individual fields and then add them.

For the first one I came up with:

E=k|q|/r^2

E1=k|-3e-3C|/1^2

E1=k(3e-3)/1

E1=2.697e7N/C

E2=k(4.5e-3C)/6^2

E2=1.12e6 N/C

2.697e7+1.12e6= 2.8e7N/C, which the answer says is wrong.

I don't understand this at all :( ]]>

An object falls a distance h from rest.

If it travels half the height h in the last 1.00 s, find:

(a) the time

(b) the height h of its fall.

(c) Explain the physically unacceptable solution of the

quadratic equation in t that you obtain.

I am trying to use the:

{y=y(initial) + v(initial) - 1/2gt^2}

equation to for example say that y = h/2 and y(initial) = h, assuming that the v(initial) is also 0m/s and g=9.81. Also, I am trying to apply the equation to the case where y = 0 and y(initial) = h/2, where t = 1s and v(initial) is unknown.

I just can't seem to get the right answer. Thanks all. ]]>

I am having problems even starting this question and was wondering if someone could at least guide me in the right direction! The question is:

What is the mass of 235 Uranium which when undergoing induced fission would produce the same amount of thermal energy as one ton (1000kg) of coal? ]]>

Who can give a detailed answer and explain why this works this way? ]]>

Here is the question give to me by my teacher:

A sample of 137Cs (half-life = 30.1 years) decays at a rate of 10^10 decays per second. How long will it take for the decay rate to decrease to 10^7 decays per second?

The work I have done so far is:

dN(t=0) = -λNo, where dN(t) = Noe^(-λt)

(Although online a website as it as Noe -λt, so not sure if λt should be raised or not)

Because I am trying to find the difference I can make this formula equal to itself:

Noe^(-λt) = Noe^(-λt)

Where:

λ is my decay constant (10^10 and 10^7)

e is e (2.71828)

t is the time (guessing at 0 and x (what the question is asking for))

No is the amount - which I do not know

Overall, the part I am confused with is if this is even correct, and if so how do I find the No of the amounts? ]]>

I'm an English major, not a physicist - never taken a physics class in my life, but I've been wondering about something, and hope for some help.

Here it is.

Is it fair to say the universe is a fixed system? By that I mean that all the matter that exists in the universe is all there is (that we know of), right?

And matter = energy.

And matter can neither be created nor destroyed.

So how is it that the rate or speed that the universe is expanding is increasing?

Wouldn't that require that the net energy of the system is increasing?

If matter can neither be created nor destroyed, and matter = energy, and the universe is a fixed system, how can the universe be expanding at an ever increasing rate of speed?

Thanks for your help. I just don't understand. ]]>

Is any "light" the same that has equal wavelengths no matter the source? In my case 1064nm (fiber laser). Would 1064nm YAG laser light or CO2 laser light be equal to the fiber laser light (not accounting for power input and assuming they could actually produce the same wavelength).

Also how does frequency come into this? I though frequency was the wavelength but obviously not since the unit has a frequency output of 20khz-300khz. Would this be on/off pulses?

I know I'm not a student but I need some knowledge so I can make an educated decision to protect our eyes and I bet you guys and gals can probably answer my questions.

Specs on the unit (in case some needs to know)

Power(W): 30w

Wavelength: 1064nm

Laser frequency range : 20khz-300khz

Thank you in advance.

Neal W ]]>

Since the vector forces applied to the center plate are normal to the surface, is there a lateral/shear force when sliding the center plate in and out?

I have tried to do this. I have no access to plates thick enough with rounded edges to prevent corona discharge nor a holder to get the plates close enough without the sheets being pulled into contact. If there is some lateral force then there would be an equation and no discussion or equation has been found so I am hoping someone here would know and be kind enough to share this information.

Thanks! ]]>

Sigh! My good intentions misused.

See: https://en.wikipedia.org/wiki/List_o...stream_science ]]>