Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 3.47
Baseball player Charles "Gabby" Street, a catcher for the Washington Senators, was reported to have caught a baseball thrown from a window near the top of the Washington Monument on August 21, 1908 [*]. Assume that the baseball was initially thrown horizontally, and was caught at a horizontal distance of 6.0 m and a vertical distance of 160 m below from where it was thrown. What was the initial (horizontal) speed of the ball? Neglect air resistance. Show your and explain your reasoning using properties of projectile motion.
[*] Francis Stann, "Street's Ironic Monument," Baseball Digest, vol. 10, no. 4 (April 1951), pp. 29-30.
Solution and grading rubric:
Correct. Determines the time t = 5.7 s for the baseball to fall (with no initial vertical velocity), and then solves for the initial horizontal velocity v0x = x/t = 1.1 m/s. May either directly solve for t, or other equation(s) to first solve for the final vertical velocity vy = –56 m/s.
Nearly correct, but includes minor math errors. Uses quadratic equation coefficient a = –9.80 m/s2 instead of –4.90 m/s2, or x instead of y, or sets vx = 0.
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Can at least solve for t or vy.
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at systematic use of kinematic equations for projectile motion.
Implementation of ideas, but credit given for effort rather than merit. Use of angular kinematic equations, etc.
Irrelevant discussion/effectively blank.
Sections 70854, 70855
Exam code: midterm01w4Sh
p: 35 students
r: 7 students
t: 2 students
v: 8 students
x: 1 student
y: 0 students
z: 0 students
A sample "p" response (from student 1123), solving for the final vertical velocity before ∆t:
Another sample "p" response (from student 3737), directly solving first for ∆t, with the additional baseball skills assessment of the person who released the ball from the Washington Monument: