# Posts by elena

Total # Posts: 4,389

**physics**

KE=mv²/2 v²= 2•KE/m a= v²/2s F=ma=mv²/2s= 2m•KE/2s m= = KE/s=10/0.005 =2000 N

*April 14, 2014*

**physics**

v₁ =910 m/s m₂=1000 kg v₂=10000 m/s u= 1000 m/s m₁=? (m₁+m₂)u = m₁v₁ +m₂v₂ m₁=m₂(v₂-u)/(u-v₁)= =1000(10000-1000)/(1000-910) = 100000 kg

*March 25, 2014*

**Trigonometry**

find sin2x, cos2x, and tan2x if sinx= -2/sqrt 5 and x terminates in quadrant III

*March 25, 2014*

**physics**

v=v₀+at = 10.5+(4.4•4.2) = 28.98 m/s

*March 25, 2014*

**Phyics**

1. x: ma=mg•sin α –F(fr) y: 0=-mg•cos α +N ma=0 0= mg•sin α-μN= = mg•sin α-μ•mg•cos α tan α = μ =0.4 α=arctan0.4 =21° 2. ma=mg•sin α – μ₁mg•cos α a=g&#...

*March 20, 2014*

**Physics**

The blocks move with the same acceleration ‘a’ F(fr)= μN m₁g=W₁ => m₁=W₁/g= 77/9.8=7.86 kg m₂g=W₂ => m₂=W₂/g= 114/9.8=11.63 kg x: m₁a=m₁g•sin α -μ₁N₁-T y: 0=-m₁g...

*March 20, 2014*

**physics**

1. PE=KE PE=mgh=mg•s•sinα KE=mv²/2 mg•s•sinα=mv²/2 v=sqrt(2g•s•sinα) = =sqrt(2•9.8•1.8•sin22°)=3.64 m/s v=at => a=v/t s=at²/2= vt²/2t=vt/2 t=2s/v=2•1.8/3.64 =0.99 s 2. t₁=2t=0.99...

*March 20, 2014*

**Science**

p=mv=20•5 =100 kg•m/s

*March 20, 2014*

**Physical Science**

(60 W•24hours •30 days)/1000=43.2 kW•h 43.2•0.1$=4.32$

*March 20, 2014*

**Physics**

T=ma=mv²/L m=TL/v²

*March 20, 2014*

**Physics**

An angular speed ω=v₁/R₁=v₂/R₂ v₁/v₂= R₁/R₂=9.8/6.6 =1.48

*March 20, 2014*

**Physics**

T=ma=mv²/R=1.9•2.8²/2.3= 6.48 N

*March 20, 2014*

**Physics**

B= μ₀•I/2π•d= μ₀•q•t/2π•d q=2π•d•B/ μ₀•t= =2π•28•7.3•10⁻⁵/4π•10⁻⁷•2.2•10⁻³=4.64•10⁶ C

*March 20, 2014*

**Physics**

L is the length of the solenoid N is the number of turns d is the diameter of the wire r is the radius of the solenoid (of the turn) Resistance R=ρx/A=4ρx/πd² ρ=1.6•10⁻⁸ Ω•m μ₀=4π•10⁻⁷ H/m U...

*March 20, 2014*

**MATH**

explain how to construct a perpendicular bisector

*March 12, 2014*

**Science**

the process in which body cells are duplicated in order to grow and repair body tissues is called

*March 6, 2014*

**Physics**

p=mv

*February 27, 2014*

**physics**

W=mg

*February 27, 2014*

**physics**

mg =ma =mv²/R v=sqrt(gR)=sqrt(9.8•0.6)=2.4 m/s

*February 26, 2014*

**Physics**

Work W=F•s•cosθ cosθ= W/F•s= 43/60•2=0.358 θ=69° ma=Fcos θ a=v²/2s= 2.7²/2•2 = 1.82 m/s² m= Fcos θ/a=60•0.358/1.82 =11.8 kg

*February 26, 2014*

**Physics**

Q=mλ=6.68•335000=2.24•10⁶ J

*February 26, 2014*

**Physics**

F =G•m₁•m₂/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg², F=6.67•10⁻¹¹•0.005•10/0.25=...

*January 22, 2014*

**Physics**

mgsinα=F sinα=F/mg=3.06x10^6/1.39x10^4 =0.022 α= 1,26 degr

*January 13, 2014*

**Physics**

T=1/f=1/2= 0.5 s

*January 13, 2014*

**physics**

h=gt²/2 t=sqrt(2h/g) x=v(x) •t => v(x) =x/t=x/sqrt(2h/g) = =8.3/sqrt(2•4.3/9.81)=8.9 m/s

*January 11, 2014*

**Physics**

v= v₀+at=30.55-0.805•20=14.5 m/s =14.5•3600/100=52.04 km/h

*January 11, 2014*

**Physics Classical Mechanics Help ASAP**

http://cnx.org/content/m14614/latest/

*January 10, 2014*

**physics**

mgh=mv²/2 v=sqrt{2gh} =sqrt{2•9.8•2.9} =7.5 m/s v(fin)=v-at v(fin)=0 a=v/t x=vt -at²/2=vt/2 mv²/2 =W(fr) = F(fr) •x => F(fr)= mv²/2x = 2mv²/2 vt=mv/t = =70•7.5/0.58 = 905.2 N

*January 10, 2014*

**physics**

a) W+Fx =80•0.882=70.56 J b) W=KE =mv²/2 v=sqrt(2W/m) = sqrt(2•70.56/15)=3.07 m/s c) KE=W(fr) =F•x F=W(fr)/x=KE/x=F/x = 70.56/0.045=1568 N

*January 9, 2014*

**physics**

W/A =Y(ΔL/L) ΔL=W•L/A•Y= =mg•L/πr²•Y

*January 7, 2014*

**Physics help quick!**

The force is directly proportional to 1/r2 where r is the distance. 19 AU 9.8 N/kg

*January 7, 2014*

**science**

q=K(ΔT/Δx)WL= =0.84•19•0.9•1.5/0.004 =5386.5 W

*January 7, 2014*

**physics**

Weight on one foot =480/2=240 N Pressure under her soles =Weight/area = =240/area of one sole

*January 5, 2014*

**physics**

240N

*January 5, 2014*

**physics**

PE=W(fr) kx²/2=μmgd d= kx²/2μmg= =124•2.1²/2•0.7•7•9.8 =5.7 m

*January 5, 2014*

**physics**

m₁v₁-m₂v₂=-m₁u₁+m₂u₂ u₂= (m₁v₁-m₂v₂+m₁u₁)/m₂= =(1250•30-2000•25+1250•10)/2000 = 0

*January 5, 2014*

**Need help World Geography**

1.B 2.D http://en.wikipedia.org/wiki/Slum

*January 4, 2014*

**Physics**

A) W=∫F•dx=-∫kx•dx (limits ↓0↑x) =kx²/2 or ΔW=F•Δx =-kx •Δx, W=ΣΔW= Σ(-kx•Δx)= =- kx Σ{(0-x)/2}= kx²/2 B) W= kx²/2=80•0.35/2 =14 J

*January 3, 2014*

**physics**

h=gt²/2 => t=sqrt(2h/g) =sqrt(2•73/9.81) =3.86 s v(y) = gt = 9.81•3.86 =37.87 m/s v=sqrt{v(x)²+v(y)²} =sqrt{37.87²+40²}=55.08 m/s p=mv=Pv/g =177•55.08/9.81 =993.85 kg•m/s tan α =v(y)/v(x) =37.87/40 =0.947 α=arctan0.947...

*January 3, 2014*

**AP Calculus AB**

y´=3(cosx)²(-sinx) -3(sinx)²cosx= = - 3 sinx cosx(cosx+sinx)

*January 3, 2014*

**Need help World Geograpy**

3A 6C 7C 10B 12C 13D 17D 18B 20B

*January 3, 2014*

**Physics**

P=Fv=mav a=P/mv=4300/900•13.8=0.35 m/s²

*January 2, 2014*

**physics**

PE=KE mg(H+h) =mv²/2 v=sqrt{2g(H+h))

*January 2, 2014*

**Physics**

P=Fv=mav a=P/mv=4300/900•13.8=0.35 m/s²

*January 2, 2014*

**Physics**

Q =q•W•L•t= 1380•1000•1300•12•3600= =7.75•10¹³ J Q=cmΔT ΔT= Q/cm = Q/cρV=7.75•10¹³/4180•1000•1000•1300•300= =0.048 K

*January 2, 2014*

**Physics**

m₁=36 kg, c₁= 880 J/kg•K, m₂=4 kg, c₂=387 J/kg•K Q=m₁c₁ΔT + m₂c₂ΔT = = ΔT(m₁c₁ + m₂c₂). ΔT= Q/(m₁c₁ + m₂c₂)= =60000/(36•880+4•387) = 1.8 K

*January 2, 2014*

**Physics**

a=dv/dt= -b+2ct =-0.31+2.1•10⁻³•36= =-0.2344 m/s² P=Fv=ma•v = 1264•0.2344•18.36 = 5439.7 W

*January 2, 2014*

**physics**

Y=2•10¹¹ Pa ω=2πf =2π•2=4π rad/s. ma=T-mg m ω²R =T – mg T=m(ω²R+g) =m(16π²R +g)=… T/A =Y•ΔL/L ΔL=TL/AY =…

*January 2, 2014*

**physics**

V=53•10⁶ ft³=1.5•10⁶ m³ h=45720≈46000 m The density of the air ρ=2•10⁻³ kg/m³ The buoyant force is F=mg= ρVg=2•10⁻³•1.5•10⁶•9.8 =29400≈ 30000 N Answer (d) M=800 kg m...

*January 1, 2014*

**Physics**

W(horse) =W(fr) =μNs= μmgs m=W/ μ gs= 8000/0.25•9.8•62=52.7 kg If the rope is horizontal and v=const => T= F(fr) = μmg=0.25•52.7•9.8 =129 N

*January 1, 2014*

**Physics 221**

E=Δφ/Δx PE->W(work of electric field) -> KE W=e•Δφ=e•E•Δx KE= mv²/2 mv²/2= e•E•Δx v=sqrt{2•e•E•Δx/m}= =sqrt{2•1.6•10⁻¹⁹•1000•0.001/9.1•10&#...

*December 31, 2013*

**Physics**

mv²/2 = kx²/2 +μmgs ==== W(spring) = kx²/2=... E(fr) = μmgs=... v =sqrt{kx²/m +2μ gs}=...

*December 31, 2013*

**Physics - please help me..**

W(block) =kx²/2=252•0.29²/2=10.6 J W(spring) = - 10.6 J mv²/2 = kx²/2 v=x•sqrt(m/k)= =0.29•sqrt(0.395/252) =0.0115 m/s

*December 31, 2013*

**physics**

KE(rot)=Iω²/2 =MR²ω²/2•2 KE(tr)=0.25•KE(rot) KE(tr)=0.25•MR²ω²/4 mv²/2 = MR²ω²/16 v=(Rω/4)•sqrt{2M/m)=4.5 m/s C. 4.5 m/s

*December 30, 2013*

**physics**

M= 5.97•10²⁴ kg m=500 kg r = 6.378•10⁶ m. R= 2• 0⁶ km= 2• 10⁹ m GmM/r-GmM/R = mv²/2 GM(1/r -1/R) = v²/2 v=sqrt{2GM(r-R)/rR}= =sqrt {2•6.67•10⁻¹¹• 5.97•10²⁴(2• 10&#...

*December 27, 2013*

**science**

During 1 period El→Mag→El→Mag→El => T= 4•2 μs= 8 μs=8•10⁻⁶ s f=1/T=1/8•10⁻⁶=1.25•10⁵ Hz

*December 26, 2013*

**physics**

v=sqrt{2•6.67•10⁻¹¹•1.5•1.98•10³º/10⁴}= =1.99•10⁸ m/s ≈2•10⁸ m/s

*December 25, 2013*

**physics**

C. M=1.5•1.98•10³º kg G =6.67•10⁻¹¹ N•m²/kg² mv²/2=GmM/R v=sqrt{2GM/R}=2•10⁸ m/s

*December 25, 2013*

**Physics**

PE ->KE KE ->PE(spring) => PE= PE(spring) mgh=kx²/2 x=sqrt(2mgh/k)=… PE(spring) -> KE->PE => the same ‘h’ (due to the absence of friction)

*December 25, 2013*

**Physics**

ApWeight = mg±mv²/R

*December 24, 2013*

**Physics**

mv²/R=mg v=sqrt(gR)

*December 24, 2013*

**Physics**

a=g•tanθ T= sqrt{(ma)²+(mg)²}= =m•sqrt{a²+g²}

*December 24, 2013*

**Physics**

1. PE(B)=KE+PE(A) mgh= KE+mg2R KE= mgh- mg2R= =mg(h-2R) 2. mgh= mv²/2+mg2R v²= 2g(h-2R) a= v²/R= 2g(h-2R)/R 3. mgh= mv²/2+mg2R h= v²/2g +2R

*December 24, 2013*

**physics**

The total energy at the top point is mv²/2+mg2R. It is equal to the energy at lower point. Its height is h=R-Rcosθ = R(1-cosθ) => the total energy is mv₁²/2 +mgR(1-cosθ). Use the law of conservation of energy. mv²/2+mg2R = mv₁²...

*December 24, 2013*

**physics**

E=h²n²/8ma² Read http://www.umich.edu/~chem461/QMChap3.pdf

*December 23, 2013*

**physics**

V=8000cm³=8•10⁻³m³ p=2 atm= 2.03•10⁵Pa T=273 K ν=pV/RT = 2.03•10⁵•8•10⁻³/273•8.31 = = 0.716 moles V=const p₁/T₁=p/T p₁=T₁p/T=373•2.03•10⁵/273 =2.77•10&#...

*December 23, 2013*

**physics**

Δp•Δx≥h Δx=d=10⁻⁵ Δp•d ≥h Δp≥h/d=6.63•10⁻³⁴/10⁻⁵=6.63•10⁻²⁹ b. change in p greater or equal to 10^-29 kg m/s mΔv•Δx≥h Δx=d = m =...

*December 23, 2013*

**physic**

a= v²/R=420²/430 =410.2 m/s² F=ma=1750•410.2 =717907 N

*December 22, 2013*

**physics**

α=25º, β =35º, m=80 kg, μ=0.7 Fcosβ - F(fr) - mgsin α = 0 N+Fsinβ – mg cos α = 0 N= mg cos α - Fsinβ F(fr) = μN = μ(mg cos α – Fsinβ) Fcosβ -μ(mg cos α – Fsinβ) - ...

*December 21, 2013*

**physics**

My mistake in the last line =1.22•10⁻¹¹ m=12.2 pm

*December 20, 2013*

**Physics 11 Forces Unit**

1. F =G•m₁•m₂/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg², F =G•m₁•m₂/R²= =6.67•10⁻¹¹•(4.15•10⁸)²/60²=3191 N 2. g`=GM/R²= =6....

*December 19, 2013*

**Physics AP**

cos φ=0.25/1.2 =0.208 => φ=78° sinφ=0.98, tan φ=4.7. x: ma=Tcosφ y: 0=Tsinφ-mg a=v²/R, Tsinφ=mg Tcosφ= mv²/R Tsinφ/Tcosφ= mgR/ mv² tanφ= gR/v² v=sqrt{gR/tanφ}=sqrt(9.8•0.25/4.7) =0.72 m...

*December 19, 2013*

**physics**

KE=10⁴•1.6•10⁻¹⁹ =1.6•10 ⁻¹⁵J KE=mv²/2 =m²v²/2m =p²/2m => p=sqrt(2m•KE) λ=h/p =h/sqrt((2m•KE)= =6.63•10⁻³⁴/sqrt(2•9.1•10 ⁻³¹•1.6&#...

*December 19, 2013*

**physics**

a=v²/s=51²/75 =34.68 m/s²

*December 18, 2013*

**PHYSICS**

ma=F-μ mg a=F/m -μg

*December 18, 2013*

**physics**

a=μ(k)g s=v²/2a

*December 18, 2013*

**physical**

2) power

*December 18, 2013*

**physics**

↧W=m(g-a) ↥W=m(g+a)

*December 18, 2013*

**magnetis**

a. collapse (shorten)

*December 18, 2013*

**magnets**

Work=0

*December 18, 2013*

**PHYSICS URGENT HELP**

PE=qV V-potential

*December 18, 2013*

**magnets**

Prob. 9 http://www-physics.ucsd.edu/students/courses/winter2010/physics2b/hw/hw8.pdf

*December 18, 2013*

**electricity and magnets**

http://courses.washington.edu/phys431/hall_effect/hall_effect.pdf

*December 17, 2013*

**PHYSICS**

THETA =90

*December 17, 2013*

**physics**

The current in the loop and magnetic field direction are connected according to the right hand rule: curl fingers to the direction of the current in the loop, the thumb points in the direction of magnetic moment of the loop that coincides with the direction of B. => The ...

*December 17, 2013*

**magnetism**

Let x be the distance from the right end of the rails to the rod. Magnetic field of the long straight wire is B=μ₀I/2πr If the infinitesimal horizontal strip of length x and width dr, parallel to the wire and a distance r from it => area A = x dr and the ...

*December 17, 2013*

**manetism help!**

F=qvB mv²/R=qvB R=mv/qB T=2πR/v=2π mv/qBv= =2π m/qB T1=T2 (T doesn’t depend on v)

*December 17, 2013*

**Physical science**

When the balls are moving in opposite directions v₁= {-2m₂v₂₀ +(m₁-m₂)v₁₀}/(m₁+m₂) v₂={ 2m₁v₁₀ - (m₂-m₁)v₂₀}/(m₁+m₂)

*December 17, 2013*

**Physics multiple choice**

1- b) False 2 -c) 10 N [up] 3 - d) 400 N

*December 17, 2013*

**Physics**

Constant v = 2πR/T=2π•7.3/34 = 1.3 m/s Constant centripetal acceleration is a=v²/R =1.3²/7.3 = 0.23 m/s²

*December 17, 2013*

**PHYSICS PLS HELP**

a)theta=pi/2

*December 17, 2013*

**Physics**

At the top point v=0 => time of upward motion of the 1st stone is t=v/g =22.7/9.8=2.32 s. Δt =2.32 -2.14 =0.18 s. At t=2.32 s the 1st stone is at the top point h₁=v₀t-gt²/2 =27.7•2.32 – 9.8•2.32²/2 =37.9 m with v=0 and begins its ...

*December 17, 2013*

**Physics**

PE-> KE -> PE(springs) mgh =23 kx²/2 x=sqrt{2mgh/23k} = =sqrt{2•43•9.8•1.93/23•6000} =0.012 m

*December 16, 2013*

**Physics**

F=ma E=F/e=ma/e E=Δφ/Δx => Δφ =E Δx= ma Δx /e= =9.1•10⁻³¹•10¹²•0.04/1.6•10⁻¹⁹=0.2275 V

*December 16, 2013*

**Physics Elena Help pls**

Let x be the distance from the right end of the rails to the rod. Magnetic field of the long straight wire is B=μ₀I/2πr If the infinitesimal horizontal strip of length x and width dr, parallel to the wire and a distance r from it => area A = x dr and the ...

*December 16, 2013*

**Physics**

Distance between the current I₀ and I is b=sqrt{0.015²+0.1²} =0.101 m. According to Bio-Savart Law, the magnetic fields (B₁=B₂) created by the currents lying on the ground at the point where current I is located are B₁=B₂=μ₀I/...

*December 16, 2013*

**physics-important fast**

a=v²/2s F=ma= mv²/2s

*December 13, 2013*

**physics**

v=ωR t=s/v= s/ ωR=8600/9.1•0.45=2100 s=35 min

*December 13, 2013*

**Physics-urgent**

s=v(t+3) s=at²/2 v(t+3) =at²/2 at²-2vt-6v=0 t²-10t-30=0 t=12.42 s s= v(t+3)=20(12.42+3) = 308.4 m

*December 13, 2013*