Recent content by shenwei1988

heat! so hard. true or false 1.The entropy of a system can never decrease 2.All Carnot engines are reversible 3.It is impossible have a net transfer of heat from a cold reservoir to a warm reservoir 4.A refrigerator lowers the entropy of the volume inside 5.If the temperature...

F=mg=25x9.8 for question 1.) f=Fu ---> 165=25x9.8xu find u , u is the coefficient of static friction between the chair and the floor. try to do 2 by yourself

F=mg f=mgu 165N is the static friction force 127N is the kinetic friction force simply put in the number f(s)=F*u

by the way, i am sure if we need to consider the air pressure or not.

Homework Statement On January 15, 1919, a cylindrical tank of molasses ruptured, and poured out over the streets of Boston in a 9 m deep stream. Pedestrians and horses were killed, and buildings were knocked down. Suppose the tank was 87.7 m high and 3.37 m diameter, and it was full of...

thanks a lot, the hint you gave is so helpful. i got it right.

using Newton's law of gravity, T^2= (4π^2*r^3)/GM volume of sphere is V=4/3πr^3 ρ=M/V put in Newton's law of gravity, T^2=3πV/GM T^2=3π/Gρ

my professor gave us this problem on the homework assignment about Fluid. Planet X is a sphere made entirely of the mythical metal exoferrum, which has density 2810 kg/m3. What is the period of orbit for a satellite in circular orbit just above the surface of Planet X? (That's right: I did...

Three point masses lie along a rigid, massless rod of length L = 5.61 m : - Two particles, both of mass m = 2.1 kg, lie on opposite ends of the rod. - Mass M = 7.29 kg is in the center of the rod. Assume the rod lies along the x-axis, and rotates about the y-axis. about a point 1.28 m...

A hockey puck of mass m sits on a frictionless, horizontal table tied to a string of length L. The puck starts at rest, and accelerates to some speed v moving in a horizontal circle of radius L. The net work done on the hockey puck,depend on what? L,m,or r?? i forgot the formula for the...

not, i put the value of x. and get the force, then use the force * distance.w=(6.68*2.78^2+1.56)*2.78

The magnitude of a certain one-dimensional force varies according to: F = 6.68x^2 + 1.56 where x is the displacement from the origin in meters, and F is the force in Newtons. At t = 0, a 677 g mass is at the origin moving in the positive x-direction at speed 8.46 m/s when this force begins...

yeah, i forgot to add the force of helicopter. thank you man!

is the force mg ?

A helicopter is used to lift a 72.7 kg astronaut 16.9 m vertically out of the ocean by means of a cable. The astronaut rises with constant upward acceleration of magnitude 7.23 m/s2 until she reaches the helicopter. a) How much work is done by the helicopter on the astronaut...