Phys 101 Final, Dec 12
th
, 2006
Page 1
McGill University
PHYS 101
(Introduction to Mechanics for the Life Sciences)
FINAL EXAM SOLUTIONS
2006 PHYS 101 Final exam
Examiner: K.J. Ragan
x6518
Short answer questions (answer all)
:
you should not need to do any calculations
for these questions
, and should answer in
a few words, a few short phrases, or a simple
sketch.
In some cases you might find it useful to quote an appropriate formula.
1) [2 pts]
Tarzan is perfecting the timing of his vineswinging, hoping to be able to impress
Jane. He wonders if he has to change his timing when he has Jane on the vine with him.
Assuming that the vine length is the same, what can you say about the period of the
swing of the vine when he is alone, or with Jane? Assume small amplitude swings.
Solution
: The period of a pendulum is independent of mass, for small
amplitude swings: Tarzan doesn’t have to worry about his timing (at least, not
his pendulum timing!).
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document2) [2 pts] For the two plots of velocity vs. time (v vs. t) shown below, which, if any, best
represents the motion of a ball thrown vertically up in the air and caught some time T
later?
Solution
: b). The velocity starts as a large positive number (upwards moving),
and ends as a large negative number (downwards going). The slope of a
velocity vs. time graph is the acceleration, and we know that this motion is
characterized by constant a (at 9.8 m/s
2
). So b) correctly describes the
motion.
a) describes a motion with NET displacement (the area under the curve),
velocity ALWAYS positive, and acceleration ALWAYS changing.
3) [2 pts] Would you expect sound waves, or light waves, to diffract more (ie, have a larger
diffraction angle) when they pass through the same opening such as a doorway? Why?
Solution
: You would expect sounds waves to diffract more (ie, have a larger
characteristic diffraction angle). That angle is
θ
=
λ
/D
where D is the opening
(doorway) size. Since
λ
sound
>>
λ
light
,
θ
sound
>>
θ
light
.
4) [2 pts] Two balls of different mass (but equal size) are thrown vertically upwards into the
air, with the same initial velocity. They do not collide. Which ball, if any, reaches the
greatest height ?
Solution
: They reach the same height. The initial velocity is the same, and the
final height is given by d = v
o
2
/2g, independent of mass.
5) [2 pts] A physics student plays with two examples of simple harmonic motion: a mass on
a spring and a simple pendulum. She finds that each of the two has a period of 1.0 sec.
She’s an astronaut, and on her next trip to the moon takes each along and measures the
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '08
 prof
 Force, Mass, Velocity

Click to edit the document details