PHYS 407 Exam 1A PDF

## PHYS 407 Exam 1A **PRINT CLEARLY Name:** Jazzie Juevesano **Do not open this exam until instructed.** To be completed during class Friday, September 27th from 10:10-11:00 am. Versions A and B of this exam are different. There are two parts, short answer (50 pts) and a problem (70 pts). There...

## PHYS 407 Exam 1A **PRINT CLEARLY Name:** Jazzie Juevesano **Do not open this exam until instructed.** To be completed during class Friday, September 27th from 10:10-11:00 am. Versions A and B of this exam are different. There are two parts, short answer (50 pts) and a problem (70 pts). There are a total of 120 points possible. **Equations and constants:** - $x = x_i + v_it + \frac{1}{2}at^2$ - $v = v_i + at$ - $v_f^2 - v_i^2 = 2a(x - x_i)$ - $g = -9.8 m/s^2$ The solution to a quadratic equation of the form: $ax^2 + bx + c = 0$ is $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$ **Part I: Short answer questions** 1. [5 pts] Dominic is driving at 20 m/s then applies the brakes for 2 seconds to slow down for a 10 m/s school zone. What was his acceleration while breaking? - a. -15 m/s² - b. 15 m/s² - c. 5 m/s² - d. -5 m/s² 2. [5 pts] This graph shows the position of a cart moving on a straight track versus time. What is the cart's velocity at 1.5 s? - a. 15 m/s - b. 20 m/s - c. -20 m/s - d. 10 m/s 3. [5 pts] For the graph in (2), what total distance did the cart travel? - a. 4 m - b. 30 m - c. 0 m - d. 40 m 4. [5 pts] For the graph in (2), what was the cart's total displacement? - a. 4 m - b. 30 m - c. 0 m - d. 40 m 5. [5 pts] Which velocity graph matches this motion diagram? 6. [5 pts] You throw a ball upward with an initial velocity of 2 m/s. What is the ball's velocity when it lands back in your hand? (you don't move your hand) - a. 2 m/s - b. -2 m/s - c. 0 m/s - d. Not enough information to determine 7. [5 pts] When do the objects in the graph have the same speed? - a. Sometime before t0 - b. At t0 - c. Sometime after t0 - d. Never 8. [5 pts] A cart speeds up while moving towards the origin. What do the position and velocity versus time graphs look like? 9. [5 pts] A ball rolls up a ramp and then back down. Which is the correct acceleration graph? 10. [5 pts] An object undergoes acceleration **a** while moving from point 1 to point 2. Which of the below graphs shows the velocity vector **v2** as the object moves away from point 2? **Part II: Longer problems** Choose either problem 11 OR problem 12: *Full credit for correct work at each part, even if information used from previous parts is incorrect or left symbolic (i.e. t2, a1, x2, as long as they are defined.) **11.** On Sunday, Andy Dalton of the Carolina Panthers threw a 31-yard-pass straight down the middle of the field to receiver Adam Thielen. Thielen caught the pass at the goal line, jumping off the ground, scoring their 3rd touchdown of the game against the Las Vegas Raiders. Dalton was 7 yards behind the line of scrimmage when he threw the ball, so the pass was caught 38 yards down the field. Measurements reveal that Dalton released the ball at 52 mph 20° from the horizontal, from about the same height as his head. Both players are 6 ft 2 inches tall. - a. [15 pts] Draw a picture representing the motion of the football down the field and label the distances in meters and the velocity in meters per second (there are 0.91 m in a yard, 0.30 m in a foot, and 1609 m in a mile). - b. [10 pts] Draw a vector representing the ball's initial velocity and break it into horizontal (call it x) and vertical (call it y) components. What are the initial velocities in the x and y directions? - c. [25 pts] How far down the field would the ball have landed if it was not caught? - d. [20 pts] How high did Thielen have to reach above his head to catch the ball at the goal line? **12.** You are a conductor on a freight train that is moving at 50 mph down a 5% grade when you notice the bridge is out. There are 300 meters of good track left before the train falls into the ravine. You immediately apply the brakes as hard as you can. - a. [15 pts] Draw a picture representing the motion of the train on the track. Label the initial velocity in meters per second and the grade in degrees. The percent grade measures the local slope of the track (in percent). - b. [10 pts] Draw vectors representing the acceleration of the train before the brakes are applied, the acceleration due to the brakes, and the total acceleration while braking. (These can be left symbolic, but please label clearly and make sure you accurately depict all angles.) - c. [25 pts] What is the minimum acceleration the brakes must achieve to stop the train? - d. [20 pts] You've slowed the train to 15 m/s, but the brakes fail with 200 meters of track remaining. You have to jump off of the train. Luckily, the brakes seem to be keeping the speed constant. You know from your experience as a conductor that survival rates of train jumps are very low for speeds over 20 mph (9 m/s), so you climb on the roof and run backwards on the train as fast as you can. You leap off the back of the train just as it tumbles into the ravine. What minimum speed do you need to be running when you jump to land at 9 m/s relative to the ground? How much time do you have to reach this speed? Do you think you'll survive?