omgitsme

Why do the beds in dorms have to be longer than normal?

In a simple electric circuit, Ohm's law states that V=IR , where V is the voltage in volts, I is the current in amperes, and R is the resistance in ohms. Assume that, as the battery wears out, the voltage decreases at 0.04 volts per second and, as the resistor heats up, the resistance is increasing at 0.03 ohms per second. When the resistance is 200 ohms and the current is 0.02 amperes, at what rate is the current changing? Answer in amperes/second.

I keep getting the wrong answer and I don't know if it has to do with my process or if I'm just calculating things wrong. This is what I did:

R = 200

I = 0.02

dR/dt = 0.03

dV/dt = -0.04

R*(dI/dt)+I*(dR/dt) = dV/dt

dI/dt = [(dV/dt)-I*(dR/dt)]/R = [(-0.04)-(0.02)(0.03)]/200 = -2.03e-4

apparently the answer is wrong. am I doing something wrong?

A certain storm cloud has a potential of 1.00 108 V relative to a tree. If, during a lightning storm, 60.0 C of charge is transferred through this potential difference and 1.00% of the energy is absorbed by the tree, how much sap in the tree can be boiled away? Model the sap as water initially at 30.0°C. Water has a specific heat of 4186 J/(kg·C°), a boiling point of 100°C, and a latent heat of vaporization of 2.26 106 J/kg.

I don't know where to start with this problem.

Thanks for the help.

A defibrillator is a device that applies a strong electric shock to the chest over a time interval of a few milliseconds. Electrodes called paddles, about 8 cm across and coated with conducting paste, are held against the chest on both sides of the heart. Assume an energy of 350 J is to be delivered from a 30.0 µF capacitor. To what potential difference must it be charged?

I have tried using the equation V=Q/C by using 350 J for the Q and 3e-5 F for C, but I don't know if I have my units wrong or if I'm just going at the problem in the wrong way. The answer should come out in volts, but every answer I've tried, webassign has said is wrong.

Thanks for the help.

a) Regarding the Earth and a cloud layer 750 m above the Earth as the "plates" of a capacitor, calculate the capacitance. Assume the cloud layer has an area of 1 km2 and that the air between the cloud and the ground is pure and dry.

b) Assume charge builds up on the cloud and on the ground until a uniform electric field of 4.00 106 N/C throughout the space between them makes the air break down and conduct electricity as a lightning bolt. What is the maximum charge the cloud can hold?

I don't understand where to start in setting up this problem.

Problem: Given that the acceleration vector of a particle is a(t) = -9cos(-3t)i - 9sin(-3t)j - 3tk, the initial velocity is v(0) = i + k and the initial position vector is r(0) = i +j + k, compute:

a) The velocity vector v(t) = _____i+_____ j+_____k

b) The position vector r(t) = _____i+_____j+______k

I took the integral of a(t) and got

3sin(-3t)i - 3cos(-3t)j - 3/2t^2

but i'm not too sure where to go from there. I don't really know how to use the initial velocity and position vectors.

Thanks!

I had unprotected sex twice over the past month. After the first time I took the morning after pill but after the second time I did not. The second time the guy pulled out before he *****. I have had my period after both instances, but I have heard of people having their periods even though they are pregnant. So should I take a test even though I've had my period after both instances?

I am not trying to get pregnant btw......and yes I understand that I need to use protection all the time if I want to prevent pregnancies.

An energy-efficient lightbulb, taking in 22.5 W of power, can produce the same level of brightness as a conventional bulb operating at power 100 W. The lifetime of the energy-efficient bulb is 10,000 h and its purchase price is $17.00, whereas the conventional bulb has lifetime 750 h and costs $0.420 per bulb. Determine the total savings obtained by using one energy-efficient bulb over its lifetime as opposed to using conventional bulbs over the same time period. Assume an energy cost of $0.0760 per kilowatt-hour.

In a laboratory model of cars skidding to a stop, data are measured for six trials. Each of three blocks is launched at two different initial speeds vi and slides across a level table as it comes to rest. The blocks have equal masses but differ in roughness and so have different coefficients of kinetic friction µk with the table. Rank the following cases (a) through (f) according to the stopping distance, from largest to smallest. If the stopping distance is the same in two cases, give them equal rank and list them alphabetically. (Use only the symbols > or =, for example a>b=c.)

(a) vi = 3 m/s, µk = 0.1

(b) vi = 3 m/s, µk = 0.2

(c) vi = 3 m/s, µk = 0.4

(d) vi = 6 m/s, µk = 0.1

(e) vi = 6 m/s, µk = 0.2

(f) vi = 6 m/s, µk = 0.4

How do I start this problem off? Am I suppossed to use the equation f=µ*d and then incorporate it into the equation for kinetic energy?

A 2.00 kg object placed on a frictionless, horizontal table is connected to a string that passes over a pulley and then is fastened to a hanging 7.00 kg object. Find the magnitude of the acceleration of the two objects and the tension in the string.

I'm not sure how to solve this, do I use Newton's Laws and if so how do I apply them?

A block slides down a frictionless plane having an inclination of θ = 18.7°. The block starts from rest at the top and the length of the incline is 2.55 m.

a) find the acceleration of the block

b) find its speed when it reaches the bottom of the incline

I'm not sure if I should use one of the kinematic equations to solve this?

It has been nearly a year since my first boyfriend and I broke up but I can't seem to get him out of my head. We had a good relationship until the end when I found out that he had something going on with one of my friends. In other words...he kinda cheated on me. I have tried moving on with other people and just having a good time with my other friends but nothing seems to really work.

How can I get him and that relationship out of my head so I can really move on?

Who do you think would win in the tag-team match: Cena and Batista or Big Show and the King?

I have a friend who i know likes me and has told me that. Even though he hasn't really asked me out, it kind of seems like we are going out. When people ask us if we are gf and bf, we say no because it's true, but we're not just friends either. Is it wierd to act like a couple even though we're not? What do you think about any of it?

How do you know if a guy likes you?