Physics 40 Exam 1 Fall 2014 Name: Conceptual Multiple Choice (2 pts ea): Circle the best answer. Ignore air resistance. 1. Which position vs. time curve is impossible? 2. Which photograph shows (circle the answer) i) constant positive acceleration? a) b) c) d) none ii) constant zero acceleration? a) b) c) d) none iii) some negative acceleration? a) b) c) d) none 3. In the case of constant acceleration, the average velocity equals the instantaneous velocity: a. at the beginning of the time interval. b. at the end of the time interval. c. half-way through the time interval. d. three-fourths of the way through the time interval. 4. A hunter points his rifle directly at a coconut that he wishes to shoot off a tree. It so happens that the coconut falls from the tree at the exact instant the hunter pulls the trigger. Consequently, the bullet a. passes above the coconut. b. passes beneath the coconut. c. hits the coconut. 5. Calculate the uncertainty using propagation of error, of the constant speed of a particle that travels a distance x = (58.2 ± 0.01) cm in a time t = (3.50s± 0.05) s, in cm/s. Show your calculation. a. 0.01 b. 0.02 c. 0.1 d. 0.2 e. 0.3 6. Vectors A and B have equal magnitudes. Which statement is always true? a. A + B = 0. b. A B = 0. c. A B is perpendicular to A + B. d. B A is perpendicular to A B. e. The magnitude of A B equals the magnitude of A + B. 7. Here is a position graph of an object. At t = 1.5 s, the object s velocity is A. 40 m/s. B. 20 m/s. C. 10 m/s. D. 10 m/s. E. None of the above. 8. The net distance travelled in the 4 seconds is A. 10 m B. 20 m C. 40 m D. zero 9. The net displacement travelled in the 4 seconds is A. 10 m B. 20 m C. 40 m D. zero 10. The average velocity during the 4 seconds is A. 10 m/s B. 20 m/s C. 15 m/s D. -10m/s E. zero
Multiple Choice (10 pts ea): Show work for any credit. Assume THREE significant figures for all problems. Box your final answers. Circle the BEST answer. 1. Sarah drives along a straight road at a constant speed of 30.0 m/s. She passes a parked motorcycle police officer, and one second later, the officer starts to accelerate at 4.00 m/s 2 to overtake her. Assuming the officer maintains this acceleration, determine the time it takes the police officer to reach Sarah. a. 5 s b. 15 s c. 16 s d. 17 s e. 18 s 2. An airplane moves horizontally with constant velocity of 300 m/s at an altitude of 1200m and drops a care package. How far in the horizontal direction from the release point does the package land? Ignore air resistance. a. 1280 m b. 1680 m c. 1710 m d. 3130 m e. 4700 m
3. A 0.20-km wide river has a uniform flow speed of 3.0 m/s toward the east. A boat with a speed of 8.0 m/s relative to the water leaves the south bank and heads in such a way that it crosses to a point directly north of its departure point. How long does it take the boat to cross the river? Draw the vectors representing the relative motions and write down the vector equation that goes with your vector diagram. a. 29 s b. 23 s c. 25 s d. 27 s e. 17 s 4. A hobby rocket reaches a height of 72.3 m and lands 111m from the launch point, at the same height from which it was launched. What was the angle of launch? Sketch the situation. A. 69.0 B. 67.4 C. 22.6 D. -44.8 E. 79.0
Long Problems.(20 each) Show all your work for full credit. Box and label final answers. Make it neat and easy to grade. Assume 3 significant figures. Ignore air resistance. NEATNESS COUNTS!!! 1. The a-t graph shown describes the motion of an object in the + x direction starting from rest at time t = 0 from the origin. a) Draw the v-t graph and x-t graphs above it, with the vertical axes aligned, labeling axes and value of both the velocity and the displacement at the times: t = 10s, 15s and 20 s. b) Derive an equation for position as a function of time for the interval from t = 10 s to t = 15 s. Test the equation by putting in the end points or other means. c) Find the net displacement at t = 20 s. Box it.
2 2. Tim in his Corvette accelerates from rest at the rate of (3.50iˆ 2.70 ˆjm ) / s, while Jill in her Jaguar travels with a constant velocity of ( 2.50iˆ 1.50 ˆjm ) / s. They both start at the origin of an xy coordinate system. After 5.0 s, (a) Find Tim s and Jill s position vectors, relative to the origin, expressed as ij vectors. (b) Find Jill s position vector relative to Tim s and the distance between them using these two methods: 1. The Graphical Method: Draw the vectors in a reference frame, carefully labeling everything and measure the resultant vector and report in polar coordinates. 2. Component Method: Find the resultant vector and express it polar units. Your results should agree within a few percent of each other. Calculate the percent difference of both the magnitude and the angle. Component Method Results: Graphical Method Results: Percent Difference: Graphical Method Results: