How fast could the person have to travel?

[jenita]

a person whose mass is 48 kg wishes to gain 12 kg relativistically with respect to another reference frame. How fast could the person have to travel?


the formula is as follows...
i Think M is 48 kg
mo is 12 kg
v=? can anyone help me to do this problem

 

[hage567]

Mo will be 48 kg. M will not be 12 kg, since the question states that the person wishes to gain 12 kg (so the mass will increase by this much).

I can't see the picture yet. Does it show where you are getting stuck?

 

[jenita]

sorry i don't no why the pic is not showing up...its the formula in the pic... i hope u no the formula...if mo is 48 then what is 12kg

 

[jenita]

is 12 kg M or do we have to find M first

 

[jenita]

oh you by the way c is 3.8 * 10^8

 

[jenita]

is the answer 75000000

 

[hage567]

Is this the equation you have?

$$M = \frac{M_o}{\sqrt{1 - v^2/c^2}}$$

You want to solve for v. Don't worry about the actual value of c (you've got it wrong by the way, it's 3x10^8 m/s), just leave it as "c" in your work. At the end, you can worry about converting it.

You are given Mo. You can figure out M because you know the gain in mass is 12 kg. So, what is M, then?

 

[jenita]

but to find M don't u need V

 

[hage567]

is the answer 75000000

Please show how you got that answer.

 

[jenita]

how can i solve it if i don't have M, v, and c...dont i need to have 1

 

[hage567]

but to find M don't u need V

You are trying to solve for v. You must rearrange that equation to get v in terms of the masses. It IS the equation you are using, right?

You have the information to get both masses without solving anything!

 

[jenita]

75000000...i got this by inserting 12 for M, 48 for mo and 3.08*10^8 for c...
i divided 12 from 48 which i got.25 and the squared it and got.0625... i squared 1 and c and then multiplied by c and 1 to the .0625... i was left with 5.625e15=v^2 and i squared it and got the answer... sorry it looks confusing

 

[jenita]

and yes that is the equation we are using

 

[hage567]

Like I've already said, M is not 12 kg. 12 kg is the change in the mass. So if the mass started at 48 kg and 12 kg is added relativistically, what is the new mass (M)?

 

[jenita]

oh lol...its 60 kg

 

[jenita]

so u insert 60 for m

 

[jenita]

so for M u insert 60 and then solve

 

[hage567]

oh lol...its 60 kg

There you go! Let's see what answer you get now.

 

[jenita]

i got 375000000...i did the same way like i did to get 75000000

 

[hage567]

Well that can't be right since that is faster than the speed of light. Are you using 3 x 10^8 m/s for c?

 

[jenita]

yes i am using that

 

[hage567]

Then you've gone wrong in the algebra somewhere. Can you show me your expression for v after rearranging that equation?

 

[jenita]

60/48=1.25 1.25^2== 1.5625 and then multiply with c^2 and i got 1.40625e17=v^2

 

[jenita]

and then did the square root on both sides and got that answer

 

[hage567]

No, that's not right.

Original equation $$M = \frac{M_o}{\sqrt{1 - v^2/c^2}}$$

To get v you should start by doing this (cross multiply):

$$\sqrt{1 - v^2/c^2} = \frac{M_o}{M}$$

Does that help point you in the right direction?

Don't mix up M and Mo.

 

[jenita]

i know this is stupid question...i just came across...do break the square root u have to square it then its (v2/c2) ^2..isnt it

 

[jenita]

i got 240000000

 

[jenita]

can u check in the calculator if that is right or not

 

[jenita]

i kinda did check answer by replacing .64 for V i got 62.47 for M

 

[jenita]

omg ignore this

i kinda did check answer by replacing .64 for V i got 62.47 for M