Solve Block Sliding on Plane: Coeff of Friction, Drag Force

[frenika]

Problem: A 64-lb block is released from the top of a plane inclined at 30 degrees to the horizontal. As the block slides down the plane, its coefficient of friction is 0.25, and it experiences a drag force due to air resistance equal to one-half is velocity in ft/sec. (a) Determine the equation for the velocity of the block. (b) Determine the equation for the displacement of the block, (c) Calculate the displacement and velocity of the block 5 sec after it is released. I need help setting up the equations and solving them. Thanks for your help

 

[HallsofIvy]

This looks to me like it should be in the "homework" section- and that you should show us what you have done on it yourself!

Calculate all the forces down the slope of the plane: there is a 64 pound force directly downward so the component of weight down the slope (draw the triangle) is
64 sin(30)= 32 pounds. The component of weight perpendicular to the slope is
64 cos(30)= 32 sqrt(3) pounds. You need to know that because the friction force on the block is 0.25 times that force (and, of course, is back up the slope). Finally, the air drag is (1/2)v (back up the slope).

The total force, down the slope, is 32- (0.25)(32)sqrt(3)- (1/2)v and that equals
m dv/dt (caution: m is mass N0T weight!)

 

[frenika]

I understand the formulas to use but I need help setting up the differential equation

 

[gnome]

It's very annoying when you post the same question in several forums.

 

[frenika]

it's not like you have to read every question that is posted, so who's fault is that

 

[ahrkron]

Loose the attitude. Besides, when two similar posts are made, many will try to figure out the difference, which means that duplicate posts make members loose more than just twice the time.

 

[gnome]

private message from frenika:
it's not like you have to read every message that is posted, so who's fault is that that you think it is annoying. If i wanted to i could post a message in every forum they have on this site

Suit yourself.

See how much help that gets you.

 

[quantumdude]

frenika,

If i wanted to i could post a message in every forum they have on this site

I'll refer you to the Posting Guidelines.

When posting a new topic, please select the forum that best relates to the subject matter of your topic. If you are unsure, contact a mentor or the admin. Redundant topics are not allowed and are considered spam.

And I'll also refer you to the https://www.physicsforums.com/showthread.php?t=4825.

I would also like to say that if you are looking for someone to do your homework for you, then you have come to the wrong place.

Please, for your own sake, try your homework before you come here, and show us where you got stuck. Speaking for myself, I already know that I know how to do your problem. Me doing it for you accomplishes nothing.

So, post away--and show your work!