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PHYSICS 221 SPRING 2016
EXAM 1: February 18, 2016; 8:15pm—10:15pm Name (printed): ______________________________________________ Recitation Instructor: _________________________ Section #_______ Student ID#_____________________ INSTRUCTIONS: This exam contains 25 multiple-choice questions plus 2 extra credit questions, each worth 3 points. Choose one answer only for each question. Choose the best answer to each question. Answer all questions. Allowed material: Before turning over this page, put away all materials except for pens, pencils, erasers, rulers and your calculator. There is a formula sheet attached at the front of the exam. Other copies of the formula sheet are not allowed. Calculator: In general, any calculator, including calculators that perform graphing, is permitted. Electronic devices that can store large amounts of text, data or equations (like laptops, palmtops, pocket computers, PDA or e-book readers) are NOT permitted. If you are unsure whether or not your calculator is allowed for the exam, ask your TA. How to fill in the bubble sheet:
Use a number 2 pencil. Do NOT use ink. If you did not bring a pencil, ask for one. Write and fill in the bubbles corresponding to: - Your last name, middle initial, and first name - « « Your ID number (the middle 9 digits on your ISU card) « « - Special codes K to L are your recitation section. Always use two digits (e.g. 01, 09,
11, 13). Honors sections: H1 → 02; H2 → 13; H3 → 24; H4 → 06; H5 → 42 - Fill in questions 1 through 27 for this exam
Please turn over your bubble sheet when you are not writing on it. If you need to change any entry, you must completely erase your previous entry. Also, circle your answers on this exam. Before handing in your exam, be sure that your answers on your bubble sheet are what you intend them to be. You may also copy down your answers on the table at the end of the exam and take them with you to compare with the posted answers. When you are finished with the exam, place all exam materials, including the bubble sheet, and the exam itself, in your folder and return the folder to your recitation instructor. No cell phone calls allowed. Turn off your cell phone (don’t just silence it) or leave it at home. Anyone using a cell phone must hand in their work; it will be considered academic dishonesty.
Best of luck,
Drs. Joseph Shinar, Kerry Whisnant, Kai-Ming Ho, and David Johnston
1. A constant force of 20 N does −60 J of work on a particle moving in a straight line from x = 0 to x = 5.0 m. What angle does the direction of the force make with the +x axis? A. 30o
B. 53o
C. 90o
D. 127o
E. 150o
2. An airplane is flying east at a constant speed of 550 km/h. At time t = 0, object A is dropped from the airplane. At time t = 10 s, another object B is dropped. At t = 20 s, what is the relationship between A and B (before A hits the ground)? (Neglect air resistance.) A. A is directly below B and the distance between A and B is 490 m B. A is directly below B and the distance between A and B is increasing C. A is west of and below B and the distance between A and B is 490 m D. A is west of and below B and the distance between A and B is increasing E. A is east of and below B and the distance between A and B is 490 m 3. What’s the average speed of a car that travels first 6.0 km at an average speed of 60 km/h and another 6.0 km at an average speed of 120 km/h? A. 80 km/h B. 90 km/h C. 95 km/h D. 100 km/h E. 105 km/h 4. Which one of the following vectors is perpendicular to A = 6.0 i + 11.0 j − 5.0 k? A. 2.0 i + 0 j + 3.0 k B. 2.0 i + 6.0 j − 3.0 k C. 4.0 i + 2.0 j + 8.0 k D. 5.0 i − 5.0 j − 5.0 k E. 6.0 i + 2.0 j + 3.0 k
5. At right is the x–t graph of the motion of a particle. Of the four points P, Q, R, and S, the acceleration ax is greatest (most positive) at A. point P B. point Q C. point R D. point S E. there is not enough information in the graph to decide 6. A volcano on earth can eject rocks up to a maximum height of 1000m. How high, in m, would these rocks go if a volcano on Mars ejects them with the same initial velocity? The gravitational acceleration on Mars is 3.71 m/s2. A. 1.00 x 103
B. 1.25 x 103 C. 1.63 x 103 D. 2.12 x 103 E. 2.64 x 103 -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ Problems 7 and 8 are about a particle moving in a circle of radius R = 2.00 m at constant speed v = 5.00 m/s. 7. The period of revolution of the particle is _____ s. A. 0.56 B. 1.03 C. 1.59 D. 2.07 E. 2.51
8. The magnitude of the centripetal acceleration of the particle is ____ m/s2. A. 8 .7 B. 10.2 C. 12.5 D. 14.4 E. 16.9
9. An airplane is flying with its nose pointed north with a speed of 120 mph with respect to the air. The air is moving at 50 mph in an easterly direction with respect to the ground. The speed of the airplane with respect to the ground is _____ mph. A. 130 B. 140 C. 150 D. 160 E. 170
10. A cannon ball is fired horizontally with a launch speed of 40 m/s from the top of a cliff that is 50 m above the horizontal ground. When the cannon ball hits the ground, the speed of the cannon ball is ____ m/s. (Ignore the effects of air resistance.) A. 39 B. 43 C. 47 D. 51 E. 55 11. A ball is thrown from the top of a cliff with speed v0 = 30 m/s. It lands on the ground below 7.5 s later a distance d = 100 m from the base of the cliff (see diagram). What is the height of the cliff, in m? (Ignore the effects of air resistance.) A. 74 B. 100 C. 163 D. 225 E. 276
12. Which one of the following five statements is false? (Ignore any effects of air friction.) A. The shape of the trajectory of a cannonball launched at an angle of 45˚ above the
horizontal is a parabola. B. For a particle moving in uniform circular motion, the velocity of the particle does
not change with time. C. If a baseball is launched from ground level at an upward angle, when the ball hits
the ground at the end of its flight, its speed is the same as its launch speed. D. For a particle undergoing nonuniform circular motion, the acceleration of the
particle is not directed towards the center of the circle. E. A bicycle wheel is mounted on a ring stand and is spinning. Two particles on the
wheel at different radii from the bicycle axle have the same angular speed. 13. A baseball is thrown at an upward angle of 60˚ from the ground. Which one of
the following five statements is true? (Ignore air friction) A. At the top of the ball’s trajectory, the acceleration of the ball is zero. B. At the top of the ball’s trajectory, the velocity of the ball is zero. C. At the top of the ball’s trajectory, the speed of the baseball during its flight is a
maximum. D. The time for the baseball to reach its maximum height is smaller than the time
that it takes to then come down and hit the ground. E. The time that it takes for the ball to reach its maximum height increases if the
launch angle increases above 60˚ (the launch speed does not depend on launch angle).
14. Two bodies P and Q on a smooth horizontal surface are connected by a light cord, as shown below. The mass of P is greater than that of Q. A horizontal force of magnitude F is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be
A. Greater than F B. Equal to F C. Less than F but greater than zero D. Zero E. You can’t know unless you know the value of the acceleration
15. As shown below, three blocks with mass m1 = 4.0 kg, m2 = 3.0 kg, and m3 = 2.0 kg are sliding on a surface and accelerating together due to a force of magnitude F = 36 N that pushes on mass m1 towards the right as shown in the figure. If there is no friction, what is the magnitude of the force that block m2 exerts on m3, in N?
A. 8.0 B. 12 C. 16 D. 24 E. 0 16. You walk into an elevator, step onto a scale and push the down button. Your normal weight is 625 N. If the elevator has a downward acceleration of magnitude 2.0 m/s2, the scale will read ____ N. (Assume g = 10 m/s2.) A. 625 B. 20 C. 500 D. 605 E. 645
17. Two identical masses are attached to the two ends of an ideal string, and the string is hung over a massless, frictionless pulley, as shown. What is the tension in the string? A. 0 B. mg/2 C. mg D. 2mg E. 4mg
18. Two masses, m and 3m, are attached to the two ends of an ideal string, and the string is hung over a massless, frictionless pulley, as shown. There is no friction between the larger mass and the incline. What is the acceleration of the block with mass 3m? A. 0 B. g/6, up the incline C. g/4, up the incline D. g/2, down the incine E. g/8, down the incline 19. A 2 kg box sits on a horizontal table. The coefficient of static friction between the box and the table is 0.2. An ideal string is attached to this box and to another box, and the string extends over a massless, frictionless pulley, as shown. What is the maximum value of m, in kg, such that the blocks do not move? A. 0.2 B. 0.3 C. 0.4 D. 0.5 E. 0.6
20. In the double incline shown in the figure, m2 is sliding down the incline with friction. Its free body diagram is
A.
B. C. D.
E. 21. A force F pulls a block up a rough incline (i.e., there is friction between the block and the incline) at a constant speed, as shown in the diagram. Which force has the largest magnitude of work done on the block? A. Gravity B. F C. The normal force between the block and the incline D. Friction E. F and gravity have the same magnitude of work done on the block
22. A ball is suspended from the ceiling by a rope of length 1.5 m. It swings in a horizontal circle with constant speed such that the ball is 1.2 m below the suspension point (see diagram). What is the speed of the ball, in m/s? (Use g = 9.8 m/s2.) A. 1.8 B. 2.2 C. 2.6 D. 3.0 E. 3.4 23. Two blocks of mass M are attached to the arms of a rigid cross, both a distance d from the center, as shown. The cross is rotating about its vertical axis. If the horizontal rods break when a tension T0 is applied, what is the maximum frequency, in revolutions/s, at which the rod can rotate?
A. 12π
T02
M 2gd
B. 12π
MdT0
C. 12π
gd
D. 12π
T0Md
E. 12π
M 2gdT02
24. A 4.0 kg object is moving with speed 2.0 m/s, a 2.0 kg object is moving with speed 3.0 m/s, and a 1.0 kg object is moving with speed 4.0 m/s. If the objects are brought to rest by the same constant braking force, which object travels the farthest before it stops? A. The 2.0 kg object B. The 1.0 kg object C. The 4.0 kg object D. The 4.0 kg object and the 1.0 kg object both travel the farthest E. It is impossible to know without knowing how long each force acts
25. A bucket with water of mass M is swung in a vertical circle of radius R at constant tangential speed v. That speed is the minimal speed at which the water does not spill from the bucket. The normal force on the water exerted by the bottom of the bucket at the top and bottom points of the circle are ___ and ___ , respectively. A. Mg, Mg B. 0, 2Mg C. 0, 0 D. 2Mg, 0 E. 2Mg, 2Mg 26. A person pushes horizontally on a heavy box and slides it across the level floor at constant velocity. The person pushes with a 60 N force for the first 10 m, at which time he begins to tire. The force he exerts then starts to decrease linearly from 60 N to 0 N across the remaining 5.0 m. How much total work did the person do on the box, in J? A. 450 B. 550 C. 650 D. 750 E. 900
27. A 200 horsepower engine drives a car at a constant speed of 70 mph on a flat, straight road. If half of this maximum power from the engine is used for driving the car forward, what is the drag force on the car, in N? A. 1.4 B. 3.2
C. 6.4 D. 1.1 x 103
E. 2.4 x 103
Physics 221 midterm exam 1 - KEY 1 11 21
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