AJM:5/4/09 Page 1 of 2 Score /100
Physics 131 Midterm Spring 2009
Name
PLEASE READ THIS FIRST:
• Time limit: 55 minutes
• Please remove hats and turn off and put away any communication devices.
• You may use one sheet of prepared notes (8 ½ x 11, both sides).
• Perform all of your work on blank paper and staple them together with this sheet at the front.
• Read each problem carefully and be sure to pay attention to any hints that are provided. The credit you receive
on each problem will depend more on how you get your answer than on what answer you get. There is no need
to be as “wordy” as I ask you to be on homework, but you must show your work or give at least a brief
explanation for every answer. I give no credit for unsupported ans wers. I do give partial credit for partially
correct solutions, but only when I can determine that what you are doing is partially co rrect.
• Make certain that all numerical answers are given with a reasonable number of significant digits (when in
doubt, three is usually a good compromise) and that you have included appropriate and simplified units.
• Check your answers for physical reasonableness whenever possible; I do deduct a s mall number of points for
ridiculous answers that you don’t comment on.
• Above all, DO NOT MAKE THESE PROBLEMS HARDER THAN THEY ARE! In virtually every case,
these problems are very simple to solve if you just apply the few physical principles that we’ve discussed and
do so using the orderly methods that I have demonstrated for you.
1. The Japanese bullet train has a mass of 700 thousand kilograms and accelerates from rest to 240
km/hr in about 3 minutes.
a) [5] What is the magnitude of its acceleration? [Assume it to be constant.]
b) [10] How far does it travel during the acceleration?
c) [5] What is the magnitude of the net force required to produce the acceleration?
2. The graph at right shows the velocity of a car traveling
along a straight road running west to east as a function of
time. Assuming that the car starts at the origin at t = 0:
a) [7] Find its position at
t=8 s
.
b) [7] Find its acceleration at
t=24 s
.
b) [6] Find its position at
t=40 s
.
3. Three forces are applied to a 5.0 kg object causing it to
accelerate at 3.0
m/s2
, south. Two of the forces are:
!
F
1=25 N
, east and
!
F
2=30 N, 37°
to the west
of south,
a) [5] Apply Newton’s second law to the object to find an equation that gives the third force,
!
F
3
in
terms of the other given quantities.
b) [5] Draw a reasonably careful graphical representation of the equation you obtained in part a.
Your diagram should male clear the approximate magnitude and direction of
!
F
3
.
c) [10] Find
!
F
3
in magnitude and direction format.
(more problems on the back)
