Friday
May 6, 2016

# Posts by Elena

Total # Posts: 4,383

physics
v₀ = 0 v = ω R ω=v/R =15/0.3=50 rad/s ω =εt=> ε = ω/t= 50/8 =6.25 rad/s² 2πN = εt²/2 N= εt²/4π=6.25•8²/4π= 31.8 rev
August 8, 2013

physics
ω= ω₀- εt 2πn=2πn₀ - εt ε=2π(n₀-n)/t =2π(30-20)/2=31.4 rad/s² N= εt²/4π = 31.4•2²/4π =10 rev L=2πR•N =2π•0.05•10 =3.14 m
August 8, 2013

Physics
If the net force on Charge B is zero, => the electric field strength is zero at the point B (charge B location). vector E(A) +vector E(C) +vector E(D) = 0 => At the point B: Vectors E(A) and E(C) are direcred to the right => vector E(D) has to be directed to the left...
August 8, 2013

physics
If the net force on Charge B is zero the electric field strength is zero at this point. vector E(A) +vector E(C) +vector E(D) = 0 => At point B: Vectors E(A) and E(C) are direcred to the right => vector E(D) has to be directed to the left => charge D is positive. kq(A...
August 8, 2013

science
h=gt^2/2
August 8, 2013

Physics
ma=Fcosα –F(fr) a=0 0=Fcosα – μN= Fcosα – μmg (b) F = μmg/cosα = (c) W= Fcosα•d = (d) W(fr) = μmg•d =
August 8, 2013

Physics
mass of the bullet is m = 25 kg (???) mv²/2 =F(res)•d F(res) = mv²/2d d₁= mv₁²/2•F(res)
August 8, 2013

Physical Science
1) t=s/v= 28/4 = 7 hr 2) KE=PE=mgh =7.2 •9.8•1.2 = …J 3) Q=mcΔT ΔT= Q/mc = 30000/0.39•3.9 = …
August 7, 2013

Physics
N₁=N₀exp(-λt₁) N₁/N₀ = exp(-λt₁) ln(N₀/N₁) =λt₁ λ = ln(N₀/N₁)/t₁= =ln(2/1.6)/156=0.223/156 (day⁻¹) N₂=N₀exp(-λt₂) = =2•exp(-0.223•201/156)=2...
August 7, 2013

Physics
angular distance = 880+340 =1220 degr angular displacement =880-340 =540 degr
August 6, 2013

Physics Angular Motion
ma=T-mg mv²/R=T - mg T = mv²/R + mg
August 4, 2013

Physics Angular Motion
a= v²/R v=sqrt(aR)
August 4, 2013

physical sciences
water H₂O acetone CH₃-C(O)-CH₃ ethanol CH₃-CH₂-OH or C₂H₅OH methylated spirit CH₃ OH http://en.wikipedia.org/wiki/Water http://en.wikipedia.org/wiki/Acetone http://en.wikipedia.org/wiki/Ethanol http://en.wikipedia.org/wiki/Methanol
August 4, 2013

Physics
Upward motion of the weight h =v₀t-gt²/2 v= v₀ -gt v=0 => v₀ =gt => t = v₀ /g =9/9.8 =0.92 s h = v₀²/2g =9²/2•9.8 =4.13 m Let h₀ is the height of helicopter when the weight began its motion. Then for downward motion...
August 4, 2013

physics
h=gt²/2 t=sqrt(2h/g) v(y) = gt v(x) =15 m/s v= sqrt{v(x)²+v(y)²}
August 3, 2013

physics
L=10 log₁₀ (I/I₀) I₀= 10⁻¹² W/m² I/I₀ = 10^(L/10) I= I₀•10^(L/10) = =10⁻¹²•10^(130/10)=10 W/m² I₁ = I/19=10/19= 0.53 W/m² L=10 log₁₀ (I₁/I₀) = =10 log&#...
August 2, 2013

physics
L=10 log₁₀ (I/I₀) I₀= 10⁻¹² W/m² I/I₀ = 10^(L/10)= =10^(L/10)= I= I₀•10^(L/10) = =10⁻¹²•10^(95/10) =3.16•10⁻³W/m² E= I•A•t=I•πr²•t= =3.16•...
August 2, 2013

physics
Centripetal (centrifugal ) acceleration a= 2 m/s² a=v²/R v=sqrt(aR) =sqrt(2•200) =20 m/s Centripetal force is F=ma= 2500•2 = 5000 N http://www.engineeringtoolbox.com/centripetal-acceleration-d_1285.html
August 1, 2013

physics
ΔL= L₁ - L₂ = =10 log₁₀(I₁/I₀) – 10log₁₀(I₂/I₀) = =10 log₁₀(I₁/I₂) ΔL/10 = log₁₀(I₁/I₂) I∼A² A₁/A₂=sqrt{ I₁/I }=sqrt{10^( &#...
August 1, 2013

physics
(a) L=10 log₁₀ (I₁/I₀) ΔL= L₁ - L₂ = =10 log₁₀(I₁/I₀) – 10log₁₀(I₂/I₀) = =10 log₁₀(I₁/I₂) ΔL/10 = log₁₀(I₁/I₂) I₁/I₂ =...
August 1, 2013

physics
(a) v=331.3 + 0.606•t =331.3 + 0.606•22 =344.6 m/s s=vt=344.6•0.8=275.7 m
August 1, 2013

physics
PE=KE mgh=mv^2/2 v=sqrt(2gh) KE= mv^2/2
August 1, 2013

physics
ΔL= αLΔtº Δtº = ΔL/αL= =0.1/11.8•10⁻⁶•1000=8.43º tº=0+8 =8℃
August 1, 2013

Physics
x₁=x₂=x F=F₁+F₂ F/x= F₁/x +F₂/x = F₁/x₁+F₂/x₂ => k=k₁+k₂= 35+55 = 90 N/m
July 31, 2013

solid mechanics
External diameter D=38 mm Inner diameter d=38 -2•2.5 = 33 mm E=2.05•10⁵ N/mm² A=π(38²-33²)/4 =278.8 mm² I = π(38⁴-33⁴)/64 = 44140 mm⁴ L=2300 mm P(cr) = π²•E•I/L² = = π²2.05•...
July 31, 2013

Biomechanics
h=v²/2g v=sqrt(2gh)=...
July 31, 2013

physics
T=2πsqrt(L/g) => L=T²g/4π²= =2.15²•9.8/4•π²=1.1475 m L₁=L+ΔL = L+αLΔt= =1.1475 + 19•10⁻⁶•1.1475•133 =1.1504 m T₁=2 πsqrt(L₁/g) = = 2 πsqrt(1.1504/9.8)=2.1527 s...
July 30, 2013

physics
ΔL=L₁-L = L+ΔL -L = αLΔt L= ΔL/ αΔt =0.195 m /12•10⁻⁶•50 =325 m
July 30, 2013

physics
λ=3.35•10⁵ J/kg r=2.26•10⁶J/kg Q₁=Q₂ λm₁=rm₂ m₁=rm₂/λ= 2.26•10⁶•2.32/3.35•10⁵=15.65 kg
July 30, 2013

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= 405•2.9/4.8 = 244.7(N) Torques about the point D F(S) •BD - mg•CD = 0 F(S)= mg•CD/BD = 405•1.9...
July 30, 2013

physics
(a) 0.12•I•A = P, A=P/0.12•I = 150/0.12•700 = 1.79 m². (b) 2•365.25•(9•0.150)kW•h• 3 ¢/kW•h = =2958.5 ¢
July 30, 2013

physics
λ=v/f =s/t•f=85000/12•11.5 =.... (m)
July 30, 2013

physics
λ=v/f f=v/ λ =5.25/43 =0.122 s⁻¹=7.23 min⁻¹
July 30, 2013

Physics
A: p₁=3 atm =3.04•10⁵ Pa, V₁=1 L = 10⁻³ m³; B: p₂=6 atm = 6.08•10⁵ Pa, V₂ =5L=5•10⁻³m³; C: p₃= 4.5 atm = 4.56•10⁵ Pa, V₃=11L = 11•10⁻³m³. A->B: W&#...
July 30, 2013

physical
0=mgsinα - F(fr)= =mgsinα - μN= =mgsinα - μmgcosα. μ=sinα/cosα =tanα α =tan⁻¹0.58 =30.11º
July 30, 2013

Physics
p₁/T₁=p₂/T₂ T₁=273+20 =293 K, T₂=273+58=331 K p₂=p₁T₂/T₁= ...
July 30, 2013

physics
v(x) =v₀(x) =v₀cosα =const
July 29, 2013

physics
Q=Q₁+Q₂+Q₃= =mc(ice)(27-0)+mλ(ice) +mc(water) (35-0)= =5(2060•27 + 335000 + 4183•35) = …
July 29, 2013

physics
L=L₁+L₂=L₀₁+ΔL₁ +L₀₂ + ΔL ₂= = L₀₁+α₁•L₀₁•ΔT +L₀₂ + α₂•L₀₂•ΔT= =1+ 23.1•10⁻⁶(450-25) +1+ 12•10&#...
July 29, 2013

physics
T=F(buoyancy) –mg = = ρ(water)Vg - ρ(balsa)Vg= =Vg[ρ(water) - ρ(balsa)] = =0.25³•9.8(1000 – 160)=129 N
July 29, 2013

physics
p=p₀+ρgh= 1.013•10⁵ + 800•9.8•18 = =2.42•10⁵ Pa
July 29, 2013

physics
p= F₁/A₁= F₂/A₂ F₁/π R₁²= F₂/π R₂² F₁ = F₂ R₁²/R₂²= m₂g •R₁²/R₂²= =1500•9.8 •0.005²/0.5²=1.47 N
July 29, 2013

physics
Standard reference sound intensity I₀= 10⁻¹² W/m² I₁=10⁷W/m² L=10 log₁₀ (I₁/I₀) = =10 log₁₀(10⁷/10⁻¹²) = =190 dB
July 29, 2013

physics
N=L/λ =Lf/v =10•215/130=16.5 => 16
July 29, 2013

physics
f=f₀/{1 – (v/u)}=960/{1- (34/343)} = =1065 Hz
July 29, 2013

physics
T=2πsqrt(L/g), g=4π²L/T²=4π²•0.171/0.833² =...
July 29, 2013

physics
7.7•x = 53• 1 x=53/7.7 =6.88 m
July 29, 2013

physics
N=(n₂²-n₁²)/2a=(186²-226²)/(-2•6.4)= =1287.5 rev
July 29, 2013

physics
m₁v₁ - m₂v₂ =(m₁+m₂)u u= (m₁v₁ - m₂v₂)/(m₁+m₂)= =(1.8•10³•15-9•10²•15)/(1.8•10³+9•10²)= =13500/2700=5 m/s (eastbound)
July 29, 2013

physics
0=N-m₁g => N = m₁g 0=T-F(fr) => T=F(fr)=μN= μ•m₁g 0=T-m₂g => T= m₂g -------- μ•m₁g = m₂g μ = m₂g/m₁g= 50/100 =0.5
July 29, 2013

physics
mv²/R =GmM/R² v² =GM/R M= v²R/G (the gravitational constant G =6.67•10⁻¹¹ N•m²/kg²)
July 29, 2013

physics
F=ma=mω²R ω↑=> F↑
July 29, 2013

physics
mv₀²/2= mgh h= v₀²/2g mg(H+h) = mv²/2 mgH +mv₀²/2 = mv²/2 v=sqrt{ v₀² +gH} = = sqrt{1.7²+9.8•3.2} = 5.85 m/s
July 29, 2013

physics
The 1st ball h=v₀t₁+gt₁²/2 The 2nd ball x=v₀t₂ h = gt₂²/2 t₁<t₂
July 29, 2013

physics
s=vt=90000•0.5/3600 = 12.5 m
July 29, 2013

Physics
ℰ = -N•dΦ/dt = -N•d(B₀Scosωt)/dt = = NB₀Sωsinωt, ℰ max= NB₀Sω, Without the figure, I believe that S=πR² => ℰ max= NB₀πR²ω = =100•10⁻⁶•3.14•0.1&#...
July 29, 2013

physics
ma=mω²R, ω=sqrt(a/R) = =sqrt(g/R) = =sqrt(9.8/100)=0.313 rad/s
July 29, 2013

physics
T=2πsqrt(L/g), T₁=2πsqrt(L/g₁), (T/T₁)²=g₁/g, g₁ = g(T/T₁)² =…
July 28, 2013

physics
f=1/T =1/2πsqrt(L/g)=...
July 28, 2013

physics
m₁=10 kg, m₂=m₁+62=72 kg, f₁= ω₁/2π = sqrt(k/m₁)/2 π , f₂=ω₂/2π = sqrt(m₂/k)/2 π, f₂ =f₁•sqrt(m₁/ m₂)=3sqrt(10/72)=1.12 Hz.
July 28, 2013

physics
R=0.04 m t= 0.012 m The solution is correct.May be there is mistake in calculations (or in your answer)...
July 28, 2013

physics
Newton’s 2nd law vector(ma) = vector(mg ) +vector( N) +vector(Ffr) Projections: ma=F(fr) 0=N-mg mv²/r =μN N=mg mv²/r = kN = μmg μ=v²/gr. tanα =F(fr)/N = μmg/mg = μ = v²/gr. v=sqrt{gr•tanα} T=2πR/v= 2πR...
July 28, 2013

physics
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html η=1-Tc/Th =1- 253.15/323.15 =0.2166, η = W/Qh => Qh= W/ η =3.6•10⁷/0.2166 = 1.66•10⁸ J= =39648.4 kCal 10 kW•h•10 Â¢/kW•h= 100 Â¢ (1.66&#...
July 28, 2013

physics
T=2π•sqrt(m/k) T₁²=4π²m₁/k T₂²=4π²m₂/k T₁²/T₂²=m₁/m₂ m₂=m₁T₂²/T₁² Δm= m₂-m₁ = =m₁(T₂²/T₁²-1)= =0.46...
July 28, 2013

physics
T₀=2πsqrt(L/g) = =2πsqrt(0.81/9.8)= =1.8064 s. ΔL=α•L•ΔT=19•10⁻⁶•0.81•18 =2.77•10⁻⁴m L₁=L+ ΔL =0.81+2.77•10⁻⁴= =0.810277 T₁=2πsqrt(L₁/g)= =2π...
July 28, 2013

physic
PE=KE=KE(transl) +KE (rot), mgh=mv²/2 + Iω²/2 = =mv²/2 + mR²v²/4R² =3mv²/4, mgh=3mv²/4, gLsinθ=3v²/4, v=sqrt(4gLsinθ/3).
July 28, 2013

physics
x is the length of unloaded spring F=k•Δx F=mg => m₁g=k(0.19-x) m₂g=k(0.75-x) m₁/m₂=(0.19-x)/(0.75-x) x=[0.19m₂ - 0.75m₁]/(m₂ -m₁) = =[0.19•2.8 – 0.75•0.3]/(2.8-0.3) = 0.1228 m k= m₁g/(0.19-x) = ...
July 28, 2013

physics
(a) F=k•Δx F=mg => mg=k•Δx k= mg/Δx =165/0.015 = 11000 N/m (b) m₁a=N-m₁g N=m₁(g+a) k•Δx₁= m₁(g+a) Δx₁=m₁(g+a)/k= =94(9.8+1.25)/11000=0.094 m
July 28, 2013

physics
PE=KE m₁gh =m₁v₁²/2 v₁ =sqrt(2gh) = sqrt(2•0.03•0.05) = =0.055 m/s. m₁v₁ = m₁u₁ + m₂u₂ u₂=2m₁v₁/(m₁+m₂)=2•0.03•0.055/(0.03+0.02) = 0.066 m/s. 0= u₂ -at a= u...
July 28, 2013

physics
Mg•L=2mg•x 70•0.65 = 2•30x x=70•0.65/60=0.75 m
July 28, 2013

physics
(a) mv₁²/2=0.22•N₁•Q N₁=mv₁²/2•0.22•Q = =2•10⁵•55²/2•0.22•1.3•10⁸ =10.6 gal (b) 0.22•N₂•Q= mv₂²/2 -mv₁²/2 +mgh, N₂ = m(v₂² -v...
July 28, 2013

physics
average SPEED = distance/time taken =(32.5+78)/30•60=0.062 m/s displacement = sqrt(32.5²+78²)=84.5 average VELOCITY = displacement/time taken =84.5/30•60=0.047 m/s
July 27, 2013

physics
88 km/h =88000/3600= 24.44 m/s ------ average SPEED = distance/time taken =(32.5+78)/30•60=0.062 m/s displacement = sqrt(32.5²+78²)=84.5 average VELOCITY = displacement/time taken =84.5/30•60=0.047 m/s
July 27, 2013

Physics
You can find the solution in http://www.cabrillo.edu/~cfigueroa/11/11prob_sets/Solutions/11prob_sol_5%20.pdf
July 27, 2013

MITx: 2.01x
The above answers are correct because I got a green chek and not a red X.
July 26, 2013

MITx: 2.01x
Q2_1_1 TXC=-t_0*L Q2=1_2 a) 0<=x<L ===>> (2*t_0*L)/(pi*G_0*R4) b)L<=x<=3L =>>(2*t_0*(2*L-))/pi*G_0*R^4) c) x=2*L
July 26, 2013

Physics Help ASAP
I can’t understand the direction of Observer motion (towards or from the car?). If the car and observer move towards each other, their relative speed is 25-2 =23 m/s, then f=f₀/[1-v/c)] = =520/[1-23/334] = 558.5 Hz If they move in the same direction v =25+2 = 27 m/s...
July 25, 2013

Physics Help ASAP
http://en.wikipedia.org/wiki/Doppler_effect http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html
July 25, 2013

physics
ΔL = αLΔT α =12 •10⁻⁶ °C⁻¹ ΔL = 12 •10⁻⁶•65•( -37-22) = - 0.046 m
July 25, 2013

physics
ΔL = αLΔT ΔL = 12•10⁻⁶•3•2.4•33 = 2.85•10⁻³ m ΔL/2 = 2.85•10⁻³ /2 = 1.425•10⁻³ m
July 25, 2013

physics
The volume of liquid that spills over the can is the difference between the increase in the volume of the liquid and that of the aluminum can ΔV=β₁VΔT - β ₂VΔT β₁=(ΔV/VΔT) + β ₂ = =(6.1•10⁻⁶/...
July 25, 2013

general physics
Q₁=m₁cΔT₁ Q₂=m₂cΔT₂ m₁cΔT₁=m₂cΔT₂ m₁ΔT₁=m₂ΔT₂ m₁ΔT₁=m₂ΔT₂ m (40.8 -30.9)=(190-m)(30.9-11.3) Solve for ‘m’
July 25, 2013

Physics
R=R1+R2+R3
July 25, 2013

physics
Q₁=mc₁ΔT₁ Q₂=mc₂ΔT₂ mc₁ΔT₁=mc₂ΔT₂ c₁ΔT₁=c₂ΔT₂ c₁(95-30)=c₂(292-30) c₂=c₁(95-30)/(292-30)= =840•65/262 = 208.4 J/kg•°C.
July 25, 2013

physics
mL= =m₁c ΔT m₁ = mL/c ΔT = =0.068•3.94•10⁵/4183•30.1= =0.213 kg
July 25, 2013

solid mechanics
E=205 kN/mm²= 205•10⁹ N/m². σ=E•ε(longitudinal) F/A = E•ε(longitudinal) ε=ε(longitudinal) = F/A•E= =40000/(20•10⁻³)²•205•10⁹=4.9•10⁻⁴. If a=0.2 m, b=c=0.002 m, &#...
July 25, 2013

solid mechanics
normal stress σ = F/A = 250000/0.1•0.1 = 2.5•10⁷ N/m² Tangential stress τ = F /(A/cosα) = Fcosα/A = =250000•0.5/0.1•0.1=1.25•10⁷ N/m²
July 25, 2013

Solid Mechanics
E=205 kN/mm²= 205•10⁹ N/m², μ = 0.3 σ=E•ε(longitudinal) F/A = E•ε(longitudinal) ε=ε(longitudinal) = F/A•E= =40000/(20•10⁻³)²•205•10⁹=4.9•10⁻⁴. If a=0.2 m, b=...
July 25, 2013

physics
η= 40% =>η =0.4 input heat Q₁=1.05•10¹⁴J waste heat Q₂=0.6 Q₁=6.3•10¹³ J Q₂/W=1.5 work W=0.4 Q₁=4.2•10¹³ J
July 24, 2013

physics
W=2.05•10⁸ J η= 4.00%=> η = 0,04 Q =W/0.04=5.125•10⁹ J Waste heat = Q - W = 5.125•10⁹-2.05•10⁸ = 4.92•10⁹ J N= 5.125•10⁹/6•10⁹ = 0.85
July 24, 2013

physics
Heat input Q=W+Q₁ = =8000+8000 = 16000 J η=W/Q =8000/16000=0.5 η =50%
July 24, 2013

physics
d=0.025 m Δx=0.31 m W=pΔV=p•πd²•Δx/4= =2.4•10⁵•3.14•0.025²•0.31/4 =36.5 J F=W/ Δx = 36.5/0.31 = 117.8 N
July 24, 2013

physics
0.2kcal/kg•℃=837.36 J/kg•℃ m = ρV=837.36• (a) Q=mcΔT=2.16•10⁴•837.36•10.5=1.9•10⁸ J (b) α = 2.5•10⁻⁶ /℃ ΔL = α•L•ΔT = 2.5•10⁻⁶•8.5&#...
July 24, 2013

Physics
mgH-mgh= mv²/2 v=sqrt{2g(H-h)} = …
July 24, 2013

Physics
s=(v²-v₀²)/2a
July 24, 2013

Dynamics
c.Velocity vectors before and after the collision.
July 22, 2013

Physics
λ=c/f => f=c/ λ = 3•10⁸/6•10⁻⁷=5•10¹⁴ Hz
July 22, 2013

Physics
ω=sqrt(k/m) = sqrt(20/2) = 3.16 rad/s x=Asinωt v=Aωcosωt t=0 => cosωt=1 A=v/ω =4/3.16=1.265 m x=Asinωt sinωt =x/A=1/1.265 =0.79 cos ωt =sqrt{1-sin²ωt} = 0.612 v₁=Aωcosωt =1.265•3.16•0.612 =2....
July 22, 2013

Dynamics
KE=PE+W(fr) m•v²/2 = m•g•h +F•s= =m•g•s•sinα +F•s. F=m(v²/2s - g•sinα)
July 22, 2013

BTech, Mechanical
For the 1st ball, the time of the upward motion v=v₀-gt v=0 0=v₀-gt t= v₀/g =18/9.8=1.83 s. The height of the 1st ball h= v₀t-gt²/2=18•1.83 - 9.8•(1.83)²/2= =16.53 m The time of the 1st ball downward motion before the 2nd ball begins...
July 22, 2013