Free Body Diagrams PLEASE HELP!!! 10 pts!?

Question

Can you please describe how to draw a free body diagram for the following situations (label each force you identify & include the magnitude of the force if it can be determined) THANKS!!!

A 40 kg girl sits on her stool, motionless

a small ball of a mass 0.5kg is falling through the air at terminal velocity

a cardboard box slides down a ramp angled at 25 degrees. Its mass is 55 kg and it is speeding up as it descends

Answer 1

these are hard to "draw" in these text boxes.

but here are some hints

the girl is a rest so the 40 kg down is equaled by 40kg up from the stool

http://www.glenbrook.k12.il.us/GBSSCI/PH...

the ball is not accelerating: so the .5kg down must equal the .5kg up from wind resistance ( even though the ball is moving at terminal velocity)

http://www.glenbrook.k12.il.us/GBSSCI/PH...

the box is accelerating downward at 25 deg so the component of the 55kg along the surface must be more that the friction holding it back - until it too, like the ball, gets to its terminal velocity, or hits something at the bottom of the slope,

http://en.wikipedia.org/wiki/Free_body_d...

hope this helps,

gudluk

Answer 2

Each of these is acted on by gravity.  So the force exerted by gravity (in Newtons) is equal to the mass (kg) x 9.8 N/kg or 10 N/kg depends on your teacher.

So you need to draw down arrows with attached forces of

40 x 9.8 = 392 N

0.5 x 9.8 = 4.9 N

55 x 9.8 = 539 N

The normal force is perpendicular to the surface.  So for the girl the normal force up from the stool = force of gravity down so draw an arrow equal in size to the one you drew going down for gravity but this time upwards from the stool.

In this case you have 2 arrows - 1 up, 1 down both equal in size.

2.  Similar to the girl example except here the up arrow is not a normal force but friction (or wind resistance).  So again one arrow up, one down, each represents 4.9 N.

3.  Gravity arrow straight down again, normal force perpendicular TO THE SURFACE.  Friction force going up the slope but not too long.  You would need to know the friction constant for the surface to give this a magnitude.

Answer 3

Yeah, just like draw it.

Answer 4

The normal force for the girl on the stool is actually 40kg x 9.8(gravity) it has to counteract her weight. So on a level surface like this one, the normal force is equal and opposite to her weight.

The small ball is the force of air resistance upward .5 kg and the mass downward.

the box on the incline , the normal force is perpendicular to the surface so its at 90-25 degrees to the horizontal, and is equal to the component of gravity mgcos(theta)