Statistics on first exam – Fall 05
Following the statistical summary of the results, there is an important policy change for next exam.
The grades on this exam were very low and ranged from 16 to 102, with an average of only 52.6 for both lectures combined. (The difference between the lectures was less than 2 points.) This average includes any extra credit points, and it is significantly lower than in recent years for this course, which I have taught for the last four years. But I do not consider you to be poorer students, and I explained in class why I suspected the average is much lower. If you want to see what your percentile is on the exam consult the chart below. As an example how to read the graph, if you earned a 70 on this exam that would put you in about the 80th percentile, meaning the top 20% of the class.
Of the 214 people who took the exam 72% opted to take the retest – this usually increased their grades quite a bit, although not always. The top scantron form stapled to your test is the retest, and the one below is the in-class test. Note that there were four different versions of the in-class test, with the questions arranged in different orders, whereas the retests were all the version shown below. As I mentioned in class I made a mistake in grading the retest, and had to manually correct it. If you find grading mistakes please call them to my attention all at one time, and do so as soon as possible.
Policy change for next exam.
To alleviate time pressure during the exam the in-class exam will only consist of free-form problems (no multiple choice). For the multiple choice component of the exam you will be asked to turn in a scantron form plus sheets showing your workat the start of the next class following the exam – no late forms will be accepted. You would be free in doing the multiple choice component of the exam to consult the book, your notes, and other students – but not other professors or the tutor. The take-home multiple choice questions will count 40% of the total grade. Please note that this is an experimental change in grading which may not be continued beyond this exam.
The answers for the four versions are
Vers (a): bdd(b/d)acdaacbcccdVers (b): bbdd(b/d)aaccccdcac
Vers (c): bdbd(b/d)acaaccccdaVers (d): bbd(b/d)acaccccdaad
b/d means b or d. I counted both answers as being correct because I unwisely chose them too close together. On the in-class test scantron question #50 identifies which version you took. The retest shown below was version (d).
PHYS 243mult choice
Exam1problem
Fall 2005 semesterextra credit
Name ______Total Please print
Read carefully: Do not detach the scantron form from the test itself. The multiple choice questions count four points each – 60% of total. On all questions you should assume air resistance is negligible. There is no penalty for guessing, so answer all questions. Please put your answers on both the scantrons, and directly on the exam itself on the line next to each question. For the non-multiple choice problem zero credit will be given for an answer with no work shown. You are expected to observe the GMU Honor Code. For 930 section please do not leave until the end of the period.
__b___1. Rock A is thrown off the roof of a building horizontally while rock B is dropped from the edge at the same initial height. Do the rocks stay in the air the same time? Do they have the same speed just before they land?
(a) yes, yes (b) yes, no (c) no, yes (d) no, no (e) none of them
__b____2. An object dropped from rest falls through a distance d. Its final velocity will be
(a) (b) (c) (d) (e) none of them
___d___3. An object’s whose motion is described by this v versus t graph.
has an acceleration: 30 m/s
(a) 15 m/s2 (b) -15 m/s2 (c) 7.5 m/s2 (d) -7.5 m/s2 0 4 s
___b,d___4. Which of these is the closest power of 10 to the volume of your brain in cubic meters?
(a)4 x 10-6 (b) 4 x 10-2 (c) 4 x 10-8 (d) 4 x 10-4
__a____5. The magnitude of the resultant of two vectors of fixed length is greatest when the angle between them is ______, and least when the angle is ______
(a)0, 180 (b) 45, 180 (c) 0, 90 (d) 45, 90 (e) none of them
___c___6. A mass m is acted on by a net force F, and is found to have an acceleration 2 m/s2. What would be the acceleration of a mass 2m acted on by a net for 4F?
(a)1 m/s2 (b) 2 m/s2 (c) 4 m/s2 (d) 8 m/s2 (e) none of them
___a___7. You are pushing a 5 kg box across a horizontal floor by exerting a 10 N force. What is the net force on the box if it moves at constant velocity 10 m/s?
(a)0 (b) 10 N (c) 20 N (d) 30 N (e) none of them
___c___8. In the previous question the magnitude of the force of the box on your hands is _____ the force of your hands pushing the box
(a)less than (b) greater than (c) equal to (d) more info is needed
___c___9. Under the usual sign conventions, a car which is travelling to the left and slowing down has ______velocity and ______acceleration (a) positive, positive (b) positive, negative (c) negative, positive (d) negative, negative
____c___10. Which one of these quantities is zero for a projectile at the highest point of its path?
(a)v (b) vx (c) vy (d) a (e) none are zero
____c___11. A boat heads directly across a 100 m wide river, and winds up 100 m downstream, because of the current. In this case the velocity of the boat with respect to the shore is ____ times the velocity of the current.
(a)0.71 (b) 1.00 (c) 1.41 (d) 2.00 (e) none of them
____d___12. Which of these is not a vector quantity? (a) velocity (b) displacement (c) acceleration
(d) time
See other side!
____a___13. Suppose a football is kicked from the ground and has a horizontal range of 80 m. If the ball is kicked with half the initial velocity along the same initial angle, its range will be
(a)20 m (b) 40 m (c) 80 m (d) 160 m (e) none of them
____a___14. The experiment I did in class where someone tried to catch a $5 bill before it dropped between their fingers having fallen 5 cm showed that a person’s reaction time is
(a)more than 0.1 s (b) more than 0.2 s (c) less than 0.1 s (d) less than 0.2 s
____d___15. In this course make-up exams are given (a)only when I am notified in advance (b) only when a medical reason is provided (c) only when one grade is much lower than the others (d) under no circumstances
Extra credit jeopardy question (5 pts). You must give a grammatically correct English sentence in the form of a question for this answer: written in the space below
By what factor does the range of a projectile increase when you triple its initial velocity, while keeping its samelaunch angle with thehorizontal?
Problem: A football player throws the ball releasing it 2.0 m above the ground with an initial velocity whose magnitude is 30 m/s. The ball takes 2.0 seconds to reach its highest point
(a)At what angle with the horizontal was the ball released? (13 pts)
Please note that this part was almost identical to part (a) of kicked football problem on p. 15 of the notes except I here asked you to solve for a different quantity – the initial angle instead of the max height.
At the top of its path: so:
Use: so: and
(b)Write an equation that would allow you to solve for the time the ball is in the air, but do not bother to solve it. All terms in the equation must be specified numerically except t. (14 pts)
Please note that this part was identical to part (a) of the stone off a cliff problem on p. 17 of the notes except I only asked you to get the equation not solve for t.
Use: with proper numerical values inserted this becomes:
(you were told not to solve for t)
(c)Suppose that you had found after solving (b) that the ball was in the air for 5 seconds. How far would the ball have travelled horizontally? (13 pts)
Please note that this part was identical to part (b) of the stone off a cliff problem on p. 17 of the notes
PHYS 243 Exam Announcements
- Please visit the restroom before the exam, since you will be asked to remain for the entire period.
- Be sure to turn off all cell phones and pagers.
- When you get the exam do NOT detach or bend the scantron sheet from the exam
- Put your name and answers on both the exam and the scantron. You may begin as soon as you get it.
- If you have any questions during the exam please come up to the front and ask me them.
- When I call time at the end of the exam, please stop writing immediately.
- You will be able to download the multiple choice questions from the course web site by noon today if you should want to take the retest.
Equations for first exam
1 in = 2.54cm
Correction to Jeopardy question: in the denominator should be