# Need Serious Help

1. Apr 28, 2004

### 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

2. Apr 29, 2004

### 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!)

3. Apr 29, 2004

### frenika

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

4. Apr 29, 2004

### gnome

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

5. Apr 30, 2004

### frenika

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

6. Apr 30, 2004

### ahrkron

Staff Emeritus
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.

7. Apr 30, 2004

### gnome

Suit yourself.

See how much help that gets you.

8. Apr 30, 2004

### Tom Mattson

Staff Emeritus
frenika,

I'll refer you to the Posting Guidelines.

And I'll also refer you to the Homework Help Guidelines.

Last edited: Apr 30, 2004