Tuesday, October 14, 2008

Problem 6.28

The key to this problem is to note that the tension T is the same for all segments of the rope.
Once you know this, simply draw the forces acting on the two pulleys. For example the lower pullley will feel a force 2T due to the two segments of rope pulling it UP, it will also feel a
force mg pulling it down. The net force will yield the acceleration of the box.

Monday, October 6, 2008

Problem 5.32

Before you do this problem review the elevator problem. There, the key idea is to write the equation for the forces acting on the person on the elevator:

N-W=ma

where N is the normal force: the force the scale is exerting on the person, and where a is the acceleration of the person. The scale "reads" the force exerted on it which is the normal force N.

So for the person on the boat you have 3 force measurements. One is when the boat is stationary, which should give you the persons weight, and therefore mass. The maximum force measurement (220 lb) should give you max acceleration etc. make sure you convert lb to Newtons.