Wednesday

April 16, 2014

April 16, 2014

Posted by **BB** on Thursday, March 29, 2012 at 1:33pm.

part A is the formula: f(s+v) / f(s) = √ (ms / (ms + mv))

part B. In some data, the silicon sliver has a mass of 2.10×1^0−16g and a frequency of 2.01×10^15 Hz without the virus and 2.88×10^14 Hz with the virus. What is the mass of the virus in grams?

this is my correct work problem i did below

2.10*10^-16 -[(2.88*10^14/2.01*10^15)^2*2.10*10^-16]/ (2.88*10^14/ 2.01*10^15)^2 and i got 2.1*10^14g which i got wrong ive been stuck with this problem for a while i need help

- Physics help please!!! -
**Elena**, Thursday, March 29, 2012 at 2:15pmm(v) = m(s)• [(f(s)/f(sv))^2 -1] =

=2.1•10^-16• [(2.01•10^15/2.88•10^14)^2 -1]=1•10^-14 g

- Physics help please!!! -
**BB**, Thursday, March 29, 2012 at 2:45pmthats wrong

- Physics help please!!! -
**Elena**, Thursday, March 29, 2012 at 4:02pmI found the same problem with same answer

A period of simple harmonic motion done by mass-spring system, is given by T = 2π √(m/k) and its frequency f = 1/T by f = 1/2π √(k/m).

The force constant of the spring is the same in both cases, so we write two equations:

f(s+v) = 1/2π √(k / (ms + mv) ) and f(s) = 1/2π √(k / ms). The ratio of both frequencies is f(s+v) / f(s) = 1/2π √(k / (ms + mv) ) / 1/2π √(k / ms). The force constant k and the 2π factors are cancelled out, and we obtain: f(s+v) / f(s) = √ (ms / (ms + mv)).

To get the mass of the virus, we must solve the above equation for mv. To do so, we must first square both sides of the equation to eliminate the square root: [ f(s+v) / f(s) ]² = ms / (ms + mv). We now multiply both sides by (ms + mv): [ f(s+v) / f(s) ]² (ms + mv) = ms ==> [ f(s+v) / f(s) ]² mv = ms – [ f(s+v) / f(s) ]² ms ==> mv = ms – [ f(s+v) / f(s) ]² ms / [ f(s+v) / f(s) ]² = 2.13×10^-16 g – (2.85×10^14 Hz / 2.04×10^15 Hz)² x 2.13×10^-16 g / (2.85×10^14 Hz / 2.04×10^15 Hz)² = 1.07 x 10^–14 g = 10.7 fg

- Physics help please!!! -
**BB**, Thursday, March 29, 2012 at 4:27pmi did the same way how you should me but i keep getting a wrong answer :/

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