# Posts by elena

Total # Posts: 4,389

**physics**

h=gt²/2 => t=sqrt{2h/g} => t₁=t₂

*November 18, 2013*

**Physics - pendulum**

T₁=2π•sqrt{L/g₁} T₂=2π•sqrt{L/g₂} g₂=g₁(T₁/T₂)²

*November 18, 2013*

**Physics - Oscillations**

T=2π•sqrt{m/k} T=t/N t/N=2π•sqrt{m/k} (t/2πN)²=m/k k=m(2πN/t)²

*November 18, 2013*

**physics**

F=691+89=780 N p=(F/2)/A=F/2A => A=F/2p=780/2•8.4•10⁵=4.6 10⁻⁴m²

*November 18, 2013*

**physics**

ρ=m/V =m/πr²h= =15700/π•1.35²•3.94=696 kg/m³

*November 18, 2013*

**physics**

I=mr²/2 mgh= mv²/2 +Iω²/2 = =mv²/2 +mr²v²/r²4 = = mv²/2+ mv²/4 =3mv²/4 v=sqrt{4gh/3} => c)both in same time.

*November 18, 2013*

**Physics**

5 N 8.5 N 0 N

*November 18, 2013*

**Physics**

- a force that makes the net force on an object zero - It is equal in magnitude and opposite in direction - A moving object in equilibrium continues at a constant velocity.

*November 18, 2013*

**Physics**

W = ∫F•dx = a•x + (b/2) •x² - (c/3) •x³ x=0.794 m a = 12600 N, b = 8420 N/m, c = 10100 N/m^2,

*November 18, 2013*

**Physics**

when the arrow representing the vector would point toward negative x <-- 10.4 km/h <--

*November 18, 2013*

**Physics, Elena Please Help If u can.**

I need the figure

*November 18, 2013*

**physics**

Son : m, v Father : M, u M=4m mv²/2=3Mu²/2 => mv²/2=3•4mu²/2 => v²=12 u²…..(1) mv²/2= M(u+1.8)²/2 mv²/2= 4m(u+1.8)²/2 v²= 4(u+1.8)² ….(2) Substitute v² from (1) in (2) 12 u²=4(u+1.8)&#...

*November 18, 2013*

**PHYSICS**

m₁a=m₁g-T₁ m₂a=T₂ - m₂gsinα Iε=(T₁-T₂)R => T₁-T₂ = Iε/R=Ia/R²=mR²a/2 R²=ma/2 m₁a+ m₂a= m₁g-T₁+ T₂ - =m₁g- m₂gsinα –( T₁-T&#...

*November 18, 2013*

**physics**

T=38.2 N, T₁=28.9 N, T₂=17,4 Buoyant force F In the air T = mg …. (1) In the water T₁=mg-F₁ …..(2) In the unknown liquid T₂=mg-F₂ ….. (3) Substitute (1) in (2) and (3) F₁=mg- T₁=T-T₁=38.2-28.9=9.3 N F₂=...

*November 17, 2013*

**Math- urgent**

-3 (x-8)+7x=12 -3x+24 +7x=12 4x=-12 x=-3

*November 17, 2013*

**math**

12 persons Each has 2 balloons and 3 prizes

*November 17, 2013*

**physics**

Max force the man can apply is F= F(fr)= μN=μmg=0.78•93•9.8=710.9 N Max acceleration a=F/M = 710.9/104000=0.0068 m/s²

*November 17, 2013*

**Math- urgent**

If x+4•7=-2 then x+28=-2 x=-30 If x+ 4⁷=-2 then x+16384=-2 x=-16386

*November 17, 2013*

**Math**

V=75• 135•0.03=303.75 m³= 303750 L t=V/V₀=303750/250=1215 min=20.25 hours

*November 17, 2013*

**PHYSICS HELP**

m₁a=m₁g-T₁ m₂a=T₂- F(fr) 0=m₂g-N Iε=(T₁-T₂)R =>T₁-T₂ = Iε/R=Ia/R² N= m₂g, F(fr)=μN=μm₂g m₁a+ m₂a= m₁g-T₁+ T₂- F(fr)= =m₁g- μm₂g &#...

*November 17, 2013*

**science**

a) Mg + 2HCl = MgCl₂ + H₂ b) 2K + 2H₂O = 2KOH + H₂ c) 2Li + 2H₂O = 2LiOH + H₂ d) 4Fe + 3O₂ = 2Fe₂O₃

*November 17, 2013*

**physics**

http://www.astro.queensu.ca/~tjb/hw/P10706/hw8_old.pdf

*November 17, 2013*

**Density Problem**

density ρ=m/V V=4πR³/3 kilometers -> meters!

*November 17, 2013*

**Science (Physics)**

On the Earth h=v²/2g On the Moon H=v²/2g₁ H/h= v²2g/2g₁v²=g/g₁ H=h g/g₁=24.2•9.8/1.6= 148.225 m

*November 16, 2013*

**Phyics**

v(max) =Aω= 2πA/T

*November 16, 2013*

**physics**

x=Asinωt v=Aωcosωt a=-Aω²sinωt =- ω²x=-(2π/T)²x |a/x| = (2π/T)² T=2 π sqrt{ x/a}=2 π•sqrt(0.235/2.3)=2 s.

*November 16, 2013*

**Physics**

Q=cmΔT= 4186•0.6•20 = 50232 J. ΔQ=Q₀-Q=140000-50232=89768 J m₁=ΔQ/λ=89768/335000=0.268 J M=0.6-0.268=0.332 kg

*November 16, 2013*

**physics**

http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/raydiag.html

*November 16, 2013*

**Physics**

http://mech.subwiki.org/wiki/Limiting_coefficient_of_static_friction

*November 16, 2013*

**Physics**

ma=mgsinα-F(fr)=mgsinα-μN= =mgsinα-μmgcosα μ(stat.fr) => a=0 0= mgsinα-μmgcosα μ=tanα

*November 16, 2013*

**Physics**

mg=500 N vector T + vecrorT +vector mg = 0 y-projection : 2Tsinα = mg T=mg/2sinα=500/2sin10=1439.7 N

*November 16, 2013*

**Physics**

ma=mgsinα-F(fr)=mgsinα-μN= =mgsinα-μmgcosα μ(stat.fr) => a=0 0= mgsinα-μmgcosα μ=tanα

*November 16, 2013*

**Physics**

on the Earth W= mg on the Moon W₁=mg₁=mg/6 =9=W/6 =900/6 =150 N

*November 16, 2013*

**Physics**

N=mg±Fsinα + if α is measured below the horizontal - if α is measured above the horizontal (a) mgcosα =μN μ = mgcosα/N (b) ma=Fcosα –F(fr) = = Fcosα – μN Solve for ‘a’

*November 15, 2013*

**Physics**

W = ∫F•dx = a•x + (b/2) •x² - (c/3) •x³ = =12600•0.794 +8420•0.794²/2 -10100•0.794³/3= =10004.4+2654.1-5055.7 =7602.8 J

*November 15, 2013*

**Physics**

W = ∫F•dx = a•x + (b/2) •x² - (c/3) •x³

*November 15, 2013*

**Physics**

mgh = mv²/2 v=sqrt(2gh)

*November 15, 2013*

**physics**

F(x) =17cos68-19 = F(y) = 17sin68+16.5 = F=sqrt{F(x)²+F(y)²}= tanα =F(y)/F(x)=

*November 14, 2013*

**Physics**

F(x)=93.3 +73.1cos45 +181 cos 45 = F(y)=73.1 sin45 -182sin 45 = F=sqrt{F(x)²+F(y)²}=

*November 14, 2013*

**Physics**

x: F=Tsinα y: mg=Tcosα F/mg=Tsinα/ Tcosα tanα =F/mg=67.7/14.9•9.8 = 0.46 α =arctan0.46= 24.9⁰ T=F/sinα=67.7/sin24.9=67.7/0.42=161 N

*November 14, 2013*

**physics**

a=v²/2s=22²/2•1.55 =156.13 m/s² t=v/a=22/156.13=0.14 s

*November 14, 2013*

**physics**

k=F/x=21.3/0.19 = 112 N/m

*November 14, 2013*

**Physics**

m₁=6.646•10⁻²⁷ kg, v₁=3.4•10⁶ m/s, m₂=3.287•10⁻²⁵-6.646•10⁻²⁷=3.22054•10⁻²⁵ kg, v₂=? p₁=m₁v₁=6.646•10⁻²⁷•3.4...

*November 14, 2013*

**Physics**

v=v₀+at

*November 14, 2013*

**Physics**

s=(v₀²-v²)/2a v= sqrt{ v₀²-2as}

*November 14, 2013*

**physics**

τ=Iε=(2mR²/5)ε= =2•12•0.22²•12/5 =2.79 N•m

*November 14, 2013*

**Physics Classical Mechanics**

http://web.mit.edu/8.01t/www/materials/ProblemSets/Raw/old_files_fall07/ps10sol.pdf

*November 14, 2013*

**Physics Classical Mechanics`**

http://ocw.mit.edu/courses/physics/8-01sc-physics-i-classical-mechanics-fall-2010/two-dimensional-rotational-motion/two-dimensional-rotational-dynamics/MIT8_01SC_problems21_soln.pdf

*November 14, 2013*

**physics**

R₀=8 Ω, T₀=20℃, R₁=8.4 Ω, T₁=70℃, T₂ = - 10℃ R₂=? R=R₀[1-αΔT] R₁=R₀[1-αΔT₁] 8.4=8[1+(70-20)α] α={8.4/8 – 1)/50 = 10⁻³ K⁻¹ R₂=R...

*November 13, 2013*

**physics Important please**

R₀=8 Ω, T₀=20℃, R₁=8.4 Ω, T₁=70℃, T₂ = - 10℃ R₂=? R=R₀[1-αΔT] R₁=R₀[1-αΔT₁] 8.4=8[1+(70-20)α] α={8.4/8 – 1)/50 = 10⁻³ K⁻¹ R₂=R...

*November 12, 2013*

**physics Important please**

q=It=Ut/R

*November 12, 2013*

**Phyics**

W=mg=ρVg= ρπr²hg= =2.2•10³•π•0.55²•1.9•9.8 = =38929 N=173173 lb

*November 12, 2013*

**phyics**

F₁=kx₁ F₂=kx₂ F₁/F₂=x₁/x₂ F₂=F₁x₂/x₁

*November 12, 2013*

**physics**

KE=W(resistive force) mv²/2 = Fs F= mv²/2s

*November 12, 2013*

**physics**

mv²/R =mg v=sqrt(gR)

*November 11, 2013*

**Physics**

do=15.1 cm, R=8.55 cm, H= 6.7 cm di= ? h=? 1/do – 1/di = -2/R 1/di = 1/do+2/R = 1/15.1 +2/8.55. di= 3.33 cm The virtual image is smaller and closer to the mirror than the object h/di =H/do => h=H•di/do = 6.7•3.33/15.1 =1.48 cm

*November 11, 2013*

**Physics please HELP**

KE=Iω²/2 =I•4π²/2T² T=2 π•sqrt{I/2•KE} If KE↓ => T↑

*November 11, 2013*

**physics**

C=ε₀A/d C=q/U=> q=CU = ε₀AU/d E=σ/2ε₀ =q/A•2ε₀= = ε₀AU/d•A•2ε₀=U/d The same result may be obtained from E=-gradΔU => E=ΔU/Δx =U/d

*November 11, 2013*

**Physics please HELP**

KE=Iω²/2 =I•4π²/2T² T=2 π•sqrt{I/2•KE} If KE↓ => T↑

*November 11, 2013*

**physics**

Energy = PE = PE₁₂+PE₁₃+PE₁₄+PE₂₃+PE₂₄+PE₃₄= =kq₁q₂/a +kq₁q₃/a+kq₁q₄/a+ kq₂q₃/a+kq₂q₄/a +kq₃q₄/a . Since q₁=q₂=q₃=q...

*November 11, 2013*

**PHYSICS(HELP)**

Prob # 7 ocw.mit.edu/courses/physics/8-01sc-physics-i-classical-mechanics-fall-2010/two-dimensional-rotational-motion/two-dimensional-rotational-dynamics/MIT8_01SC_problems21_soln.pdf

*November 11, 2013*

**physics**

F=ma=mΔv/Δt=m[v₂-v₁]/Δt= =0.38•[-1.9-2.3]/3•10⁻³ = - 532 N ( direction: from the wall)

*November 11, 2013*

**Physics falling ladder**

http://www.mathematische-basteleien.de/ladder.htm

*November 11, 2013*

**physics**

a=v²/2s

*November 11, 2013*

**Phyics**

T=2π•sqrt(L/g) L=T²g/4π² = =8.36²•9.8/4π²=17.35 m

*November 11, 2013*

**physics**

q₁ = 3 e, q₂ = 12e, q₃ = 5e The electric field at the midpoint is E= kq₂/(x/2)²- kq₁/(x/2)²= =k(12e-3e)/(x/2)² =k36e/x² (directed to the 3e charge) F= q₃E=k36e•5e/x²= =k•180e/x², where k =9•10&#...

*November 11, 2013*

**physics**

q₁ = 3 e, q₂ = 12e, q₃ = 5e The electric field at the midpoint is E= kq₂/(x/2)²- kq₁/(x/2)²= =k(12e-3e)/(x/2)² =k36e/x² (directed to the 3e charge) F= q₃E=k36e•5e/x²= =k•180e/x², where k =9•10&#...

*November 10, 2013*

**physics**

q₁ = 3 e, q₂ = 12e, q₃ = 5e The electric field at the midpoint is E= kq₂/(x/2)²- kq₁/(x/2)²= =k(12e-3e)/(x/2)² =k36e/x² (directed to the 3e charge) F= q₃E=k36e•5e/x²= =k•180e/x², where k =9•10&#...

*November 10, 2013*

**Physics Part 2**

m₁=m₂=m=0.17 kg, α=45° v=5.6 m/s, v₁=3.5 m/s, v₂=? vector p =vector p₁+vector p₂ p₂=sqrt{p₁²+p²-2p₁•p•cosα} = =m•sqrt{3.5²+5.6²-2•3.5•5.6•cos45°} = =m•...

*November 10, 2013*

**PHYSICS (HELP)**

R=2 m, Ic=9000 kg•m², r₀=1.2 m, m=20 kg, F=200 N, Δt=18 s. I=Ic+2I₀=Ic+2m r₀² = =9000+2•20•1.2²=9057.6 kg•m². M=Iα α=M/I=FR/I =200•2/9057.6 = 0.044 rad/s² ω=α•Δt =0.044•...

*November 9, 2013*

**additional science: physics**

m=F/g=1.94/9.7=0.2 kg g=GmM/(R+H)² g₀=GmM/R² =9.8 m/s²

*November 9, 2013*

**physics**

the gravitational constant G =6.67•10⁻¹¹ N•m²/kg², F =G•m₁•m₂/R²= G•m² /R² F/W=F/mg = G•m² /R²mg = G•m /R²g. mg= G•m•M/R²=> g= G•M/R² . F/W= G&#...

*November 9, 2013*

**Physics**

Distance between charges is d=sqrt{3²+3²} =4.24 cm x=d/2 =4.24/2 =2.12 cm =0.0212 m E=kq₁/x²-kq₂/x² = =k12e/x²-k3e/x²=k9e/x²= =9•10⁹•9•1.6•10⁻¹⁹/0.0212²= =2.9•10⁻⁵ N/C

*November 8, 2013*

**Physics ASAP PLease**

ΔV =V(∞)-V V(∞)=0 V=0 => ΔV = 0 Work of electric field = q₃ΔV=0 Answ. c)

*November 8, 2013*

**Physics**

KE₂-KE₁=Fs F= (KE₂-KE₁)/s=(10-8)/6 = 0.33 N

*November 8, 2013*

**Physics**

KE=W =Fs =0.8•0.5 = 0.4 J

*November 8, 2013*

**Physics**

W=mg=1768•9.8 = …N

*November 8, 2013*

**Physics**

KE=mv²/2

*November 8, 2013*

**Physics Important please**

E=kq₁/x²=kq₂/(3-x)² 3e/x²=12e/(3-x)² 9-6x+x²=4x² 3x²+6x-9=0 x²+2x-3=0 x=1 cm

*November 8, 2013*

**Physics**

KE=W(fr) mv₀²/2=F(fr)s=μmgs s= v₀²/2μg v=v₀-at v=0 => a= v₀/t s=v₀t-at²/2= = v₀t- v₀t²/2t= v₀t/2 t=2s/v₀=2v₀²/2μgv₀= =v₀/μg=6/0.1•9.8 =6.12 s

*November 8, 2013*

**PHYSICS**

KE=PE mv₀²/2=mgh=mgs/sinα s= v₀²sinα /2g= =5.5²sin23°/2•9.8 =… v=v₀-at v=0 => a= v₀/t s=v₀t-at²/2= = v₀t- v₀t²/2t= v₀t/2 t=2s/v₀=….

*November 8, 2013*

**Physics**

ΔV =V(∞)-V V(∞)=0 V=0 => ΔV = 0 Work of electric field = q₃ΔV=0 Answ. c)

*November 8, 2013*

**PHYSICS**

(a) The equations of the motion: - of the cylinder Iε =M Ia/R =TR T= Ia/R² - of the object m₂a=m₂g-T m₂a=m₂g- Ia/R² a(m₂+ I/R²) =m₂g a= m₂g/ (m₂+ I/R²) (b) T= Ia/R²=Im₂g/ R² (m₂+ I/...

*November 8, 2013*

**phy**

1/do+1/di=1/f 1/di= 1/0.21 – 1/1 = 3.76 di=0.26 m D=di+do =0.26+1 = 1.26 m (b) 1/do+1/di=1/f di =f•do/(do-f) D=do+di = =do+ f•do/(do-f) =do²/(do-f) For finding D(min) let differentiate D(do) D´={do²/(do-f)}´={2•do(do-f) -do²(1-f)}/(...

*November 8, 2013*

**physics**

Vector sum of two vectors at right angles p=sqrt{p₁²+p₂²} =sqrt2 =1.41 kg•m/s

*November 8, 2013*

**Physics Classical Mechanics**

Problem 7.9 http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/assignments/sol7.pdf

*November 7, 2013*

**Science**

http://www.lenntech.com/periodic/elements/as.htm http://en.wikipedia.org/wiki/Arsenic

*November 6, 2013*

**Science**

- The age of a solid object - to measure absolute time - measure how long it takes for unstable nuclei to turn to more stable nuclei

*November 6, 2013*

**physics**

η = W/Q =1- (T(cold)/T(hot)) W= ηQ =0.67•5900 =3953 J

*November 6, 2013*

**PHYSICS**

http://phys.thu.edu.tw/~ycchen/physics/ebook-8.01x/chapter24_physical_pendulum_v03.pdf

*November 6, 2013*

**Physics ASAP PLease**

http://www.univsul.org/Dosekan_Wanekan_D/Third%20Examination%20and%20its%20Solutions.pdf

*November 6, 2013*

**physics**

http://www.physicsclassroom.com/class/circles/u6l3d.cfm

*November 6, 2013*

**physical**

F₀cosα=ma₀ (x) a₀ (x) =F₀ cosα/m=200•0.707/3.9 =36.3 m/s² F₀ sinα =ma₀ (y) a₀ (y) = F₀ sinα/m=200•0.707/3.9 =36.3 m/s² a(y)= a₀ (y)-g =36.3-9.8 =26.5 m/s² a=sqrt(a₀ (x)&#...

*November 5, 2013*

**Physics**

d=sqrt(s₁²+s₂²) = sqrt(49+100) =12.2 km

*November 5, 2013*

**phyics**

(a)W=kx k=W/x=829/0.538 = 1540.9 N/m (b)W₁=kx₁=1540.9•0.390 =600 N

*November 5, 2013*

**Math Help? Check my answers.**

1. r/5 = 9/21 r = 9 r = 2.14 r = 11.66 r = 37.8 2. A recipe calls for 3 cups of flour to make 3 dozen cookies. Use the proportion to calculate how much flour is needed to make 9 dozen cookies. 3cups/3dozen = xcups/9dozen 6 cups 3.5 cups 9 cups 12 cups 3. Chase sold 48 tickets ...

*November 5, 2013*

**physics**

h= v₀t + gt²/2 gt²+2v₀t-2•h = 0 9.8t²+2•10t- 2000=0 t=[20±sqrt{400+4•9.8•1000}]/2•9.8 = =(20±199)/19.6 => t=11.2 s.

*November 5, 2013*

**physics**

m₁=2.4 kg, m₂=1.4 kg, v₁=4.6 m/s, v₂=0 m₁v₁= (m₁+m₂) u u= m₁v₁/(m₁+m₂) =2.4•4.6/(2.4+1.4) =2.9 m/s At the edge of the table, two boxes have kinetic (KE) and potential energy (PE), and near the ground...

*November 5, 2013*

**physics**

I₁=6A, I₂=8 A, b=0.14 m. (a) B₁=μ₀I₁/2πb=4π•10⁻⁷•6/2π•0.14=8.57•10⁻⁶ T (b) F₂ =I₂B₁Lsinα α=90° =>sinα=1 F₂/L =I₂B₁= =μ&#...

*November 5, 2013*

**PHYSICS**

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/toroid.html

*November 5, 2013*