/sci/ - Science & Math

>>11665489
>>11665501
[math] \text{pH}=-\log[\text{H}^+]=-\log1.63\cdot10^{-3}=2.79 [/math]
>>11666350
Yes.
>>11667153
Convert the speed of the car to km/min to find it travels for 120 minutes. The bus is 20% more expensive per minute, so it cost 6 pence/min. Train is three times as fast as the car so it travels for 40 minutes. Being three times as expensive as the bus, it costs 6*3=18 p/min. At 40 minutes this is £7.20. Cycle is 1/5 as fast as the train so it travels for 40/(1/5)=200 minutes. It cost 5% as much as the bus so it costs 0.05*6=0.9 p/min. 200 min/(0.9p/min) is a cost of £1.80 for the cyclist.
The difference in running cost between train and cyclist is £7.20-£1.80=£5.40
>>11667509
So you got the right value for F7 = -4900/sin45 = -6929.7, but the FBD on the right looks whack. You have the F7 vector pointed the right direction, but you forgot the negative sign (since it is really in compression). Sum the forces in the vertical and you should get F5.sin45+F7.sin45+6600=0. This gives F5 = -1700/sin45 = -2404.2. Sum horizontal forces now. -F4-F5.cos45+F7.cos45=0. This makes F4=-3200. It makes sense that F5 and F4 are both compressive loads.

>>11555183
[math] h(xy)=h(x)h(y)=3x3y=9xy=(6+3)xy=6xy+3xy=3xy [/math]

>>11397210
I will be more quantitative than that other guy. One physical principle at play is Fourier's law, which states that the heat flux conducted through a material is proportional to the temperature gradient over that material. The human body dissipates heat at a rate of something like ~200 Watts/square meter. If you cover your whole body with a blanket, you are putting thermal resistance between yourself and your surroundings. Say you have a blanket that has a thermal conductivity of 0.05 W/m*K (typical) and a thickness of 1 centimeter. Say you want to find the lowest temperature you could exist in such that you can maintain a (surface) body temp of 37 degrees C. Then, 37-T=(200*0.01)/0.05 so T = -3 degrees C or a little below freezing. The is an extremely simplified model that does not consider the still air trapped between your body in the blanket, or any notion of wind or convection (then you need to invoke Newton's law of cooling and do some really fucked up stuff to find convection coefficients). These would tend increase and decrease the possible temperature differential, respectively.
>>11397319
yw <3
>mrs. brisby poster
also me
>>11397425
>without a connection to ground
Sorry, I misunderstood. Ideally, if you are not grounded and grab one hot wire with one hand, you hand is more or less just going to be at a constant voltage. This assumption falls apart at very high voltages because real wires have finite conductivity, and there will be a voltage drop over your hand. Current then flows through your hand per Ohm's law. There's a reason why HV workers wear Faraday suits.
>>11397440
Does it? It reminds me more of root-mean-square.