Lafayette College
Department of Physics
February 11, 2009
Physics 131 LevelIIHomework Set Section 1
Youmay discuss these problems with one or twoother students (or with your instructor), but
your final solutions should be written out by you alone. Under no circumstances should you see
another student’swritten solutions. If you have discussed these problems with anyone you must
acknowledge the collaboration at the beginning of the corresponding problem. Homework is due
in my office by 3:30 PM on the due date and solutions will then be made available on the course
web site. No homework will be accepted after this time.
Youare expected to carefully explain how, starting from basic principles, you have arrivedat
your answers. Please do not use paper with edges frayed from being ripped out of a spiral bound
notebook. If the papers are illegible or disorganized, we reservethe right to return these papers
without being graded. Unless instructed otherwise, all answers should be correct to 3 or 4 sig.
figs.
Assignment 3: Due Monday,February 16 2009
Problem 1: Consider twovectors AA and BB .Let A=4and B=3. What must be the direction
of BB relative toAA so that C,the magnitude of CC =AA +BB ,has the maximum possible value.
What is that direction if Cis to have the minimum possible value. What is that direction if Cis
to be 3. 5.
Problem 2: A radar observer on the ground is ‘‘watching’’anapproaching projectile. At a
certain instant, she has the following information: the projectile is still climbing and is moving
with a speed v0=15 0 m/s, with an angle of elevation of 30degree,and the height of the projectile
is H=500 m.Assume a flat earth and that the observer lies in the plane of the trajectory of the
projectile. Assume that she is500 meters from the point just belowthe projectile.
A] Find the distance Dbetween the observer and the point of impact of the projectile.
B] Does the projectile pass overthe head of the observer or strikethe ground before
reaching her.
Problem 3: A boywhirls a stone in a horizontal circle 1. 75meters above the ground by
means of a string which is 1. 25meters in length. The string breaks, and the stone flies offhori-
zontally,striking the ground at a point that is 6. 5 meters awayfrom the boy’sfeet. What wasthe
magnitude of the radial acceleration of the stone just before the string broke?
Continued
