Physics 211 Problem Set 6 Section: ________
Due: Friday, 03/01/02 Name: ______________________
Physics 211 Syracuse University Spring 2002
Please submit your homework on this sheet. If you need more space than is available, please attach
additional sheets of paper. Note that this assignment includes questions and problems from chapters
5, 6, and 7.
1. Solve problem 37 in Chapter 5 of Serway/Beichner. (Part c is optional and will not be graded for credit.)
(a)
(b)
(c) [optional]
See Solutions Manual and Study Guide (on reserve in library)
2. Solve problem 67 in Chapter 5 of Serway/Beichner.
(a)
For the free-body diagrams (with somewhat abbreviated labeling) see page
A.44 of the textbook. Note that there are two frictional forces drawn on the
upper (5-kg) block. One is kinetic friction (by the table or floor); the other,
static friction (by the upper block).
(b)
Considering the vertical forces first, the upward normal force on the lower
block by the table is found to be about 70 N. The (kinetic) frictional force on
the lower block by the table is therefore about
µ
N = 14 N. Given an
acceleration of 3 m/s2, the net force on the upper block must be ma = 6 N; that
on the lower block, 15 N. The former is equal to the magnitude of the static
frictional forces between the two blocks (since the upper block has no other
horizontal forces acting on it). The horizontal forces on the lower block are
thus two forces to the left of magnitude 6 N and 14 N, and an unknown force to
the right (F). All three must add vectorially to result in a net force of 15 N to
the right. The force F (which could be normal or tension) therefore has a
magnitude of about 35 N.
(c)
The static frictional force fstat on the upper block must be equal to the net force
on the upper block (i.e., 6 N). Since the normal force between the two blocks is
about 20 N and fstat ≤
µ
statN, the coefficient of static friction must be at least
fstat
/
N = 0.3.
