# Posts by Elena

Total # Posts: 4,389

**Physics**

a= v²/2s F=ma

*January 10, 2013*

**physics**

Mass per unit length m₀ = m/L, Velocity in the stretched string is v = sqrt(T/m₀) =sqrt(T•L/m), λ=v/f = sqrt(T•L/m)/f, L=f²λ²m/T

*January 10, 2013*

**Physics**

A. KE=eU=1.6•10⁻¹⁹•150 =2.4•10⁻¹⁷ J B. KE=mv²/2 v=sqrt(2•KE/m) C. a= v²/2d D. v=at t=v/a

*January 10, 2013*

**Physics**

v(x)=4•10⁶ m/s, E=150 N/C L= 6 (????) t= L/v(x) F=eE, F=ma, ma=eE a=eE/m where e = 1.6•10⁻¹⁹ C, m=9.1•10⁻³¹ kg, v(y)=at =... v=sqrt{v(x) ²+v(y) ²} =…

*January 10, 2013*

**physics**

Distance = 8+1.2+0.2+4 =13.4 miles Displacement =sqrt{(8-0.2)²+(4-1.2)²} =8.29 miles

*January 10, 2013*

**physic =)**

mv²/2=mgh h= v²/2g=.... v(fin)=v-gt v(fin)=0 t=v/g=..... t(total) =2t v(ground)=v=490 m/s

*January 6, 2013*

**mechanics- physics**

substitute 'a' in s=v₀t - at²/2 and solve for 't'

*January 6, 2013*

**mechanics- physics**

v₀ =5•10⁶ m/s v=2.1•10⁶ m/s s=2•10⁻⁴ = 2•10⁻⁶ m ------------ v= v₀-at a= (v₀-v)/t substitute 'a' in s=v₀t+at²/2 and solve for 't'

*January 6, 2013*

**mechanics_ physics**

PE -> PE(spring) mgh =kx²/2 x=sqrt(2mgh/k)

*January 6, 2013*

**mechanics_ physics**

F=3 N, F(fr) =0.6 N W(F) =F•s=3•1.2 =3.6 J W(fr)=F(fr) •s=0.6•1.2=0.72 J W(total)=W(F) –W(fr)=…

*January 6, 2013*

**physics**

dA/dt = 64πt²=128 πt=128 π•1.5=603.2 cm²/s

*January 4, 2013*

**physics**

R=4t (cm) 6=4t t=1.5 s. A=4πR²=4π(4t)²= =64πt²=64π(1.5)²=452.4 cm²

*January 4, 2013*

**Please help**

18t=30•(4-t) 18t =120 -30t 48t=120 t=120/48 =2.5 18•2.5=45 km

*January 3, 2013*

**Physics...Equilibrium (physics of a clothesline)**

α is the angle that tention T makes with vertical line tan α=5/0.2 =25 α=87.7⁰ 2Tcos α=mg T=mg/2cos α =40•9.8/2•cos87.7⁰ =4884 N

*January 3, 2013*

**physics**

initial velocity and the angle

*January 2, 2013*

**physics**

no, but it's close http://physics.gu.se/~ostlund/ffp/prehistory/Fowlers_greeks_to_galileo.pdf

*January 2, 2013*

**physics**

time

*January 2, 2013*

**physics**

If v=const => a=0 f=F(fr)+mg If f is directed vertically N=0 => F(fr)=μN=0 => f=mg

*January 2, 2013*

**mechanics -physics**

averege v =total dostance/total time = =(15•120 + 18•45)/165 =15.82 m/s

*January 2, 2013*

**Physics**

Doppler shift f₀ = f/(1- v/u) = =880/(1-3.5/343)=889.07 Hz

*January 2, 2013*

**Science 8R - HELP!**

http://wiki.answers.com/Q/What_is_the_difference_between_reflection_and_refraction

*January 2, 2013*

**Anyone Please Help!**

Let t be the time of the motion to east => 300•t=400(7-t) 300t=400•7-400t 700t=400•7 t=4 hours s=300•t=300•4=1200 km

*January 2, 2013*

**physical science**

p1=m1•v1 =2000•5=10000 km•m/s p2=m2•v2=0.009•450=4.05 kg•m/s p1> p2 Impulse F•Δt=m•Δv=linear momentum

*January 2, 2013*

**physical science**

t1=t2=sqrt(2h/g)

*January 2, 2013*

**Physics**

h/s=sinα h=s•sinα PE=KE m•g•h = m•v²/2 v=sqrt(2gh) (b) PE=KE+W(fr) m•g•h = m•v²/2 = +F(fr) •s Solve for ‘v”

*December 30, 2012*

**Physics**

At the top point F(centr) =mg

*December 30, 2012*

**Physics**

Torque= force • distance 150 • (0.5-0.2) = 100 • x x= 150•0.3/100=0.45 m (from the center or at the point 0.95 m mark)

*December 30, 2012*

**science**

a=F/m

*December 27, 2012*

**Physics-mechanics**

mv²/R=GmM/R² v=sqrt(GM/R )=sqrt{6.67•10⁻¹¹•6.42•10²³ /(3.40 •10⁶+175 000)}=3.46•10³ m/s. T=2πR/v=2•3.14•(3.40 •10⁶+175 000)/ 3.46•10³ =6.5•10³ s=1.8 h

*December 27, 2012*

**Physics-mechanics**

density ρ =M/V mg=W=GmM/R² => M= WR²/Gm. V=4πR³/3. ρ =3 WR²/4πR³Gm = =3W/4πRGm = =3•9.8/4•3.14•6.4•10⁶•6.67•10⁻¹¹•1= =5.48•10³ kg/m³

*December 27, 2012*

**science**

http://www.visionlearning.com/library/module_viewer.php?mid=37

*December 26, 2012*

**physics**

t= 2vₒ•sinα/g

*December 23, 2012*

**Physics**

(a)If we place one sheet with its polarization direction 90⁰ to the polarized light then the transmitted intensity will be zero (since I=I₀•cos²α = I₀•cos²90⁰=0). If we use 2 sheets, the 1st sheet rotates by angle α (0<...

*December 21, 2012*

**PHISIC help**

KE -> PE(of elastic deformation) -> KE

*December 21, 2012*

**physics**

F=ma=ma=mv²/2s

*December 21, 2012*

**physics**

http://www.chegg.com/homework-help/questions-and-answers/bars-equilibrium-2-m-long-weighing-92-n-string-pullingdown-bars-attached-04-m-fulcrum-left-q1768975

*December 21, 2012*

**Physics**

m1•v1+0 = m1•u(1x) +m2•u(2x) 0=-m1•u(1y) + m2•u(2y) m1•v1 = m1•u1•cos20⁰+m1•u2•cosα 0= - m1•u1•sin20⁰ +m2•u2•sinα . m1•(v1 -u1•cos20⁰)=m1•u2•cosα, .....(1...

*December 20, 2012*

**PHYSICS**

E=5 x 10^5 N/C m =9.1 x 10^-31 kg e= 1.6 x 10^-19 C ma=eE a= eE/m

*December 20, 2012*

**physics**

v1=a1•t1=5.9•4=23.6 m/s v2= a2•t2 = 4.4•6.5 = 28.6 m/s τ1 =s/v1 =200/23.6=8.47 s. τ2 =s/v2 =200/28.6=6.99 s the total time for the 1st runner 4+8.47 = 12.47 s. fir the 2nd runner 6.5+6.99 = 13.49 s

*December 20, 2012*

**PHISIC help**

As the wavelength decreases, the spreading of the wave at the edges of the aperture also diminishes => the waves will spread out less

*December 20, 2012*

**PHYSICS**

F•Δt=Δp=mΔv=m[v₂-(-v₁)]=m(v₂+v₁) m= F•Δt/ (v₂+v₁)=540•6.9•10⁻³/(42+20) = 0.06 kg

*December 19, 2012*

**Physics**

V=7.5 m/s v=1.52 m/s u=? u(x)=V(x)+v(x)= 0-vsin42⁰= - 1.52•0.67=-1.02 m/s u(y)=V(y)+v(y)= V+vcos42⁰=7.5+1.52•0.0.74=8.63 m/s u=sqrt{u(x)²+ u(y)²}=8.69 m/s tanβ = u(x)/u(y)=1.02/8.63=0.12 β =6.74⁰ (west of north)

*December 19, 2012*

**Physics**

Q₁=Q₂ => cm₁(t₁-t) = cm₂(t-t₂) m₁(t₁-t) = m₂(t-t₂) Solve for ‚t“

*December 17, 2012*

**Physics**

a=(v²-v₀²)/2s=v²/2s F=ma

*December 17, 2012*

**Physics**

P=E/t=F•x/t=F•v

*December 17, 2012*

**physics**

m₁ =0.55 kg,t₁ =96.7℃ c₂=4186 J/kg•℃, m₂=2.19 kg, t₂=4.4℃ t= 7℃ Q₁=c₁m₁(t₁-t) Q₂=c₂m₂(t-t₂) Q₁=Q₂ => c₁m₁(t₁-t) = c₂m₂(t-t&#...

*December 17, 2012*

**physics**

m₁ =0.55 kg,t₁ =96.7℃ c₂=4186 J/kg•℃, m₂=2.19 kg, t₂=4.4℃ t= 7℃ Q₁=c₁m₁(t₁-t) Q₂=c₂m₂(t-t₂) Q₁=Q₂ => c₁m₁(t₁-t) = c₂m₂(t-t&#...

*December 17, 2012*

**Pysics**

m₁ =0.55 kg,t₁ =96.7℃ c₂=4186 J/kg•℃, m₂=2.19 kg, t₂=4.4℃ t= 7℃ Q₁=c₁m₁(t₁-t) Q₂=c₂m₂(t-t₂) Q₁=Q₂ => c₁m₁(t₁-t) = c₂m₂(t-t&#...

*December 17, 2012*

**physics**

efficiency of Otto engine is e= 1 –{V₂/V₁}^(γ-1) γ=(i+2)/i For diatomic gas i=5 =>γ=7/5=1.4 V₁/V₂= CR (compression ratio) e= 1 –{1/CR}^(γ-1)=1-{1/CR} ^0.4 0.331 = 1-{1/CR} ^0.4 Solving for CR, we obtain CR=2.73

*December 17, 2012*

**physics**

CoP=4.5 CoP=Qh/(Qh-Qc)=1/{1-(Qc/Qh)}=4.5 Qc/Qh=0.78 Qc=46.1 cal Qh= Qc/0.78 = 46.1/0.78=59.1 cal

*December 17, 2012*

**physics**

c₁=129 J/kg•℃, m₁ =2.6 kg,t₁ =90℃ c₂=4180 J/kg•℃,m₂=0.21 kg, t₂=23℃ t=? Q₁=c₁m₁(t₁-t) Q₂=c₂m₂(t-t₂) Q₁=Q₂ => c₁m₁(t₁-t) = c&#...

*December 17, 2012*

**physics**

F= mv²/R

*December 17, 2012*

**physics**

Q=cm(t₂-t₁) Q= 1502 J, m=0.032kg, t₁=29℃ c=387 J/kg•℃ Solve for t₂

*December 17, 2012*

**physics**

Increasing the wavelength of the light, Changing the metal, Decreasing the frequency of the light

*December 17, 2012*

**science**

a=F/m

*December 16, 2012*

**science**

Incomplete question

*December 16, 2012*

**physics**

Points: left end - A, Sam - B, center of mass - C , Joe - D , right end - E Torques about the point B: mg•BC –F(J) •BD =0 F(J) =mg•BC/BD= 430•2.8/4.6 = 261.7(N) Torques about the point D F(S) •BD - mg•CD = 0 F(S)= mg•CD/BD = 430•1.8...

*December 16, 2012*

**Physics**

m=W/g=W1/g1 g1=g•W1/W

*December 16, 2012*

**physics**

W=KE₂-KE₁=mv₂²/2 -mv₁²/2= =0.5m(v₂² - v₁²) Law of conservation of angular momentum I₁ω₁=I₂ω₂ (m₁ r₁²)(v₁/r₁)=(m₂ r₂²)(v₂/r₂) v&#...

*December 16, 2012*

**physics**

KE2-KE1=W(fr) =F•s mv₂²/2 - mv₁²/2 = F•s Solve for F

*December 16, 2012*

**science**

Please see the Related Questions below

*December 16, 2012*

**Physics**

W₀=mg g=GM/R². W=mg´, g=GM/(R+h)² ΔW= W₀-W gravitational constant G =6.67•10⁻¹¹ N•m²/kg², Earth’s mass is M = 5.97•10²⁴kg, Earth’s radius is R = 6.378•10⁶ m.

*December 16, 2012*

**Physics**

ω₀=2πn₀=2π•2000/60 rad/s ω=2πn =2π•150/60 rad/s ω=ω₀-εt ε= (ω₀-ω)/t=…. L₀=I ω₀=… L=I ω=… L(ave) =(L+L₀)/2

*December 16, 2012*

**physics**

ma= F(fr)= μN =μmgcosα a= μgcosα

*December 16, 2012*

**physics**

L=Iω I(hoop) =mR² I(sol.cyl)= mR²/2 I(sol.sph) =2 mR²/5 I(hol.sph) =2 mR²/3

*December 15, 2012*

**Physics**

E=mc²=320•10⁻⁶•9•10¹⁶=2.88•10¹³ J E/3.65•10⁷=2.88•10¹³ /3.65•10⁷=7.9•10⁵ L 7.9•10⁵•12.75=1•10⁷ km

*December 15, 2012*

**Physics**

v(n+1) = {v´+v(n)}/{1+(v´•v(n)/c²} v2= {v´+v1}/{1+(v´•v1/c²}= ={0.5c+0.5c}/{1+(0.5c•0.5c/c²} =0.8c. v3={0.8c+0.8c}/{1+(0.8c•0.8c/c²}...0.929 c v4=...=0.97561c, v5=...= 0.9918c v6=...=0.99726c, v7=...=0.99909c > 0....

*December 15, 2012*

**Physics**

0= - mg+N+Fsinα => N=mg-Fsinα => F(fr) =μN =μ(mg-Fsinα) ma=Fcosα-F(fr) = Fcosα - μ(mg-Fsinα) a=0 Fcosα =μmg- μFsinα F(cosα + μsinα)=μmg F= μmg/(cosα + μsinα)= …

*December 15, 2012*

**Physics**

0= - mg+N+Fsinα => N=mg-Fsinα => F(fr) =μN =μ(mg-Fsinα) ma=Fcosα-F(fr) = Fcosα - μ(mg-Fsinα) a=0 Fcosα =μmg- μFsinα F(cosα + μsinα)=μmg F= μmg/(cosα + μsinα)= …

*December 15, 2012*

**physics**

(a) p=mv km/h -> m/s !!! (b) F=ma=mv/t

*December 15, 2012*

**Physics**

rest energy of electron m₀c²=0.512 MeV E=mc²=1533 MeV mc² =m₀c²/sqrt(1-β²)... (1) τ=τ₀/sqrt(1-β²) …..(2) Divide (1) by (2) mc²/τ= m₀c²/τ₀ τ₀=τ• m₀...

*December 15, 2012*

**physics**

t=sqrt(2h/g) L=v• t

*December 15, 2012*

**Physics**

ma=mgsinα –F(fr) = mgsinα – μmgcosα a= g(sinα – μcosα ) = 9.8• (0.59-0.16•0.81)=4.5 m/s² The speed after the first 5 sec is v=at= 4.5•5=22.5 m/s If the net force=0, a=0 => 0 = mgsinα – μ&#...

*December 15, 2012*

**science**

(a) V=2.68 L = 0.00268 m³, t=37°C => T=310 K, p=743 torr =99058.246 Pa R=8.31 J/mol pV=nRT n= pV/RT = 99058.246•0.00268/8.31•310 =0.1 mol N= n•N₀=0.1•6.02•10²³=6.02•10²² molecules (b) V=5•10³ L=5 m...

*December 15, 2012*

**Physics**

Fick’s Law M= -D•(Δρ/Δx)•A, where M = m/t = mass flux [kg/s], D= 4.9•10 ⁻⁹ m ²/s is the diffusion coefficient (diffusivity) [m²/s], Δρ/Δx is the gradient of density [kg/m⁴], A is the area [m²]. ...

*December 15, 2012*

**physical science**

v₁= {-2m₂v₂₀ +(m₁-m₂)v₁₀}/(m₁+m₂) v₂={ 2m₁v₁₀ - (m₂-m₁)v₂₀}/(m₁+m₂)

*December 15, 2012*

**Physics**

The law of conservation of angular momentum L₁ = L₂ {(MR²/2) +(mR²)}ω₁ ={(MR²/2) +(mr²)}ω₂ ω₂=ω₁{(MR²/2) +(mR²)}/{(MR²/2) +(mr²)}= =2{60•4/2 + 32•4}/(60•4/2+ 32•...

*December 14, 2012*

**physics**

Doppler effect Frequency (observed) f=c/λ=3•10⁸/5.87•10⁻⁷=5.11•10¹⁴ Hz Frequency (apparent) f´=c/λ´=3•10⁸/5.9•10⁻⁷=5.085•10¹⁴ Hz f'=cf/(c+u) u=c{(f/f´)-1} =1.53...

*December 14, 2012*

**physics**

I = P/A = P/4πr² = 100/4π(8)² = 0.12 W•m⁻² If the sound intensity level is halved to a value of I = 0.06 W•m⁻², the sound intensity level will decrease by 3 dB. I = P/4πr² = 100/4π(x) ² = =0.06 W•m&#...

*December 14, 2012*

**physics**

F=mg g=F/m=236/63=3.746 m/s² h=gt²/2 t=sqrt(2h/g)=sqrt(2•2.1/3.746)=1.06 s.

*December 14, 2012*

**physics**

I = P/A = P/4πr² = 100/4π(8)² = 0.12 W•m⁻² If the sound intensity level is halved to a value of I = 0.06 W•m⁻², the sound intensity level will decrease by 3 dB. I = P/4πr² = 100/4π(x) ² = =0.06 W•m&#...

*December 14, 2012*

**physics**

λ=4L=4•0.9=3.6 m f=v(sound)/ λ

*December 14, 2012*

**physics**

(a) Stretch in the spring is L₁=sqrt(x²+L₀²) = sqrt(0.7² +0.5²)=0.86 m Elongation is Δx= L₁-L₀= 0.86-0.5=0.36 m. E(total) = PE=2•k•Δx²/2=2•37.7•0.36²/2=4.9 J. (b) PE=KE =mv²/2 v=sqrt(2&#...

*December 14, 2012*

**physics**

m1= 443 kg, m2=181 kg, F(fr) = F =G•m1•m2/R², μ•m2•g= G•m1•m2/R², μ•g= G•m1/R², R =sqrt(G•m1/ μ•g).

*December 13, 2012*

**physics**

see the Related Questions below

*December 13, 2012*

**physics**

mg=GmM/R² g=GM/R² g´=GM/(R+h)² g´= 0.337g GM/(R+h)² =0.337• GM/R² R²/0.337=(R+h)²= R²+2Rh+h² h²+2Rh - 1.96R² = 0 h=- R±sqrt{R²+1.96 R²}= =-R±1.72R h=0.72R=0.72•6.38•10⁶...

*December 13, 2012*

**physics**

F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg²,

*December 13, 2012*

**physics**

m1= 443 kg, m2=181 kg F(fr) = F =G•m1•m2/R² μ•m2•g= G•m1•m2/R² μ•g= G•m1/R² R =sqrt(G•m1/ μ•g)

*December 13, 2012*

**Physics**

http://ca.answers.yahoo.com/question/index?qid=20101003132118AAicaXe

*December 13, 2012*

**physics**

v=sqrt(T•L/m) λ=v/f => f=v/λ= sqrt(T•L/m)/ λ f₁/f₂={sqrt(T₁•L/m)/ λ}/{sqrt(T₂•L/m)/ λ} (f₁/f₂)² =T₁/T₂ T₂=T₁(f₂/f₁)² (T₂-T₁)/T₁=(...

*December 13, 2012*

**Physics**

s=v₀t+at²/2, v₀= 4.5 m/s, a= 0.04 m/s², t= 12s

*December 13, 2012*

**Physics**

a=(v-v₀)/t=v/t F=ma

*December 13, 2012*

**physics**

http://ca.answers.yahoo.com/question/index?qid=20110714100031AAk4Hfp

*December 13, 2012*

**Physics**

Find answer in the Related Questions

*December 12, 2012*

**Physics**

C=q/U =Ne/U , N=CU/e=55•10⁻ ¹²•5.3/1.6•10⁻ ¹⁹ =1.82•10⁹

*December 12, 2012*

**Physics**

closed end – node open end - antinode => A quarter of the wavelength is on the length of the pipe => λ=4L=4•0.6 = 2.4 m λ=v/f f=v/ λ=340/2.4 =141.5 Hz

*December 12, 2012*

**Physics**

A) 141.5 Hz

*December 12, 2012*

**physics**

From similar triangles: Hi/di =Ho/do => Hi/Ho=di/do =M

*December 12, 2012*

**physics**

mgh =179 m=179/mg =179/0.296•9.8 = 61.7 kg

*December 12, 2012*

**Physics**

Magnetic field due to the long wire B₁=μ₀I/2πb=4π•10⁻⁷•20/2•π•0.003=1.3•10⁻³ T ( B₁ is directed normal to the axis of solenoid) B=sqrt(B₁²+B₂²) =sqrt{(1.3•10⁻...

*December 12, 2012*