Recent content by anhchangdeptra

Oh sorry, in this case I'm talking about drag force caused by air resistance

Hi, I know that the drag force on an object: Fd= 1/2 . ρ . v^2 . Cd . A where A is the reference area. But in the case of a streamlined body, I don't know what will be taken as the reference area. Should it be the largest cross-sectional area of the body?

Oh yes! I really forget the M. Thank you very much!

Oh! So we only care about the smaller shell with radius= R/2. The distance from mass m to the center is r so basically we have the same formula as for an object outside the bigger shell= (GMm)/r^2 (only the r is different is the two cases)?

Imagine all the mass of the Earth is in a shell of a thickness of R(earth)/2. So if the object is inside the shell or outside the shell, I know I can apply the shell theorem to solve the gravitational force acting on it. But, what if the object is IN the shell, in another words...

Oh thank you SteamKing and Voko I know how to do it now. My problem is that I was stuck with the idea that the magnitude of r(t) is always R so I thought I must use another equation rather than r(t). Thanks a ton!

I am sorry I really don't know how to express that mathematically. I have just calculate its speed to be Rαt but I can not make an equation because the object has an increasing acceleration (because its angular accel is constant). This is quite new to me.

Homework Statement An object travels counterclockwise on a circular path with radius R and constant angular acceleration α, so that vector r(t) = R cos(αt^2/2) i^+ R sin(αt^2/2) j^  Homework Equations b. Find the time T when the object made a single revolution and returned to...