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Unformatted text preview: True/False 24/ 90/ Fall 2004 Last Name a 6’ ‘
Physics 2750
Exam #1 First Name ID # Points for each question are indicated in parentheses. F or full credit show your work for solutions to
questions that require calculations. Explain from where you start to solve the problem and show your
math ﬂowing from it for full credit. If you need more space to ﬁnish a question, write BPP (Back of the
Previous Page) at the end of the space provided and then complete your work on the back of the previous
page. For multiple choice questions, circle the letter for the answer which you believe to be correct. In all problems take the gravitational acceleration g = 10 m/sz. Each multiple choice question is worth 3 points.
1. A person initially at point P in the illustration stays there a moment and then moves along the axis to Q ’g\‘ and stays there a moment. She then runs quickly to R, stays there a moment, and then strolls slowly back
to P. Which of the position vs. time graphs below correctly represents this motion? Circle it. ~‘ position
4 (arbitrary units) O
._..
N
0.) position position position {1% time ll time M time
x o 3 position position [position 4 5 6 2. If you jumped out of a plane, you would begin speeding up as you fall downward. Eventually, due to wind resistance, your velocity would become constant in time. After this occurs, the magnitude of the
force of Wind resistance is
3 Equal to force of gravity acting on you
( b) Is much smaller than the force of gravity acting on you
c) Is slightly smaller than the force of gravity acting on you
d) Is greater than the force of gravity acting on you 3. A rocket is ﬁred vertically upward with a constant acceleration greater than g (there is no air resitance).
The rocket engine runs for several seconds and then stops. Which of the following statements is true if
we plot the velocity of the rocket as a function of time?
a) It will be parabolic
3 b) It will be a straight line
c) It will consist of two straight line segments both with positive slope
It will consist of two straight line segments with slopes of opposite signs. erson stands on a scale 1n a free falling elevator. The reading on the scale 1s
Zero
*The person’s true weight c) More than the person’s true weight d) Less than the person’s true weight, but not zero 5. An object has a velocity directed to the right, and an acceleration directed to the left. Which statement
is true?
The position of the object is increasing to the right with time, and its speed is decreasing b) The position of the object is not changing in time c) The position of the object is increasing to the left with time, and its speed is increasing (1) The position of the object is increasing to the right with time, and its speed is increasing 6. A stone is thrown vertically upwards, reaches a highest point, and returns to the ground. When the
stone is at the top of its path, its acceleration
a) Is zero
, b Is directed upwards
€55 Is directed downwards
1
l d) Changes direction from upwards to downwards 7. A, rock sits on your toe. Which of the concepts is most important in determining how much it hurts?
' a), The mass of the rock
@The weight of the rock
0) Both the mass and the weight of the rock are important
(1) Either the mass or the weight, as the two are related by a single multiplicative constant g. 8. Because some students dared to point out mistakes I have made in lectures, I have decided to give you
the following challenging problem. The First Law of Physics 2750 1s:
@ Dorina IS always right.
33 On exams you always get the only problems you don’ t know how to solve.
If you discover that Dorina 1s wrong, you must remember answer A.
a? Accumulate enough points to pass Physics 2750. 9. Write true or false by each one of the following statements:
MC‘O a) Since vectors always have positive magnitudes, the sum of two vectors must have a magnitude 25® greater than the magnitude of either one of them. x
g 2 b) If an object stops moving at a point, then its acceleration must be zero at that point
c) You throw a stone vertically upward, and it feels no air resistance. Once it is free of your hand but
% moving upward, the two forces acting on it are the downward pull of gravity and the upward force
due to its motion.
d) A car is being towed at constant velocity on a rough horizontal road using a horizontal chain. The
tension in the chain must be equal to the weight of the car in order to maintain constant velocity.
e) A stone rolls down a sloping hillside. The normal force that the surface of the hill exerts on the
stone is equal to the stone’s weight. 10. A basketball player, about to dunk the ball, jumps 80 cm vertically from the ground. A) What is his
initial speed? B) How much time does the basketball player spend in the air? C) How much time does the
player spend in the top 15 cm of this jump (going up and coming down)? Don’t forget, the basketball
player is a point particle with no dimensions! 11. The velocity of a particle moving along the x axis is given for t > O by vx = (8  6t2) m/s, Where t is in
s. What is the acceleration of the particle when (after t = 0) it passes through the origin? V739ka LMOQQ ‘t 05W X901 {A [3%
our _. , All? 39” 0le 3) §7§: Hoyt .5.) X: 3%"; av, ’““>\On’ l2 2 2M {'7 @ 12 A particle of mass 0.5 kg is subjected simultaneously to two forces, F1 and F2 = i— 33' (in N). Initially, at t = 0, the particle is at the origin and starts moving from rest with constant acceleration. If the position
oftheparticle att=2 s isr =—8i+2j , ﬁnd: a) its acceleration a at t = 2 s b) its velocity v at t = 2 s. c) force F1 4 *5) 13. A 100 kg box sits in the back of a ﬂatbed truck. The coefﬁcients of ﬁ'iction between the box and the bed of the truck are us = 0.4 and pk = 0.2. Draw a pictorial representation of the problem and a free body
diagram for all forces acting on the box. What is the maximum acceleration the truck can have without the box slipping? Bonus question: (5 points) In outer space, an astronaut is working with two pieces of equipment that on the outside look identical.
However, one of the objects has a larger mass than the other. Since objects are weightless in space (no
force of gravity, g = O III/82), how can the astronaut distinguish between the two objects? ...
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 Spring '08
 kozstin
 Physics

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