Physics 1020.90 Lab Homework 1/19/11 Spring ‘11 Road Trip Kinematics Many people have experience solving problems like these. If you can, try to do these first couple of problems without reading your textbook. 1. It is 245 mi from St. Paul, MN to Des Moines, IA. The speed limit on I-35 is 65 mph along this stretch. How long (i.e. how much time) does it take you to drive from one city to the other? If your answer is not in whole hours, round to two decimal places, and write the answer as hr + min as well. You may round to the nearest minute. 2. Continuing on I-35, you head to Kansas City, MO. It takes you 2 hrs 54 minutes, and you’re able to zip along at 65 mph the entire way. How many miles are between Des Moines and Kansas City? 3. Oklahoma City, OK is another 355 miles down I-35. Leaving Kansas city at 8:30 AM, you arrive in OKC at 3:20 PM, with a 45 minute stop for lunch along the Kansas Turnpike. How fast were you driving? 4. After a snack and a break, you leave Oklahoma City at 3:15PM, heading West on I-40. The speed limit on I-40 is 75 mph, though in Texas it drops to 65 mph after dark. It is 150 miles from OKC to Texola, OK (on the TX-OK border), and another 110 miles from Texola to Amarillo, TX. The sun sets at 5:45 pm. What time do you get to Amarillo, assuming no stops? (We will revisit this problem at the beginning of lecture next week.) 5. Looking at the first three problems, assign the terms “distance,” “velocity,” and “time” to the various components. Using those variables (distance, velocity, time; or d, v, t), rewrite the equations you solved in those problems (i.e. in the first problem, you solved for time. Write an equation that looks like time = distance (…) velocity, where (…) represents whatever mathematical operation you performed between distance and velocity. Addition, subtraction, multiplication or division are likely candidates.) 6. 1 mile = 1.609 km. 1 hour = 3600 s. Convert the speed 65 mi/hr in to units of meters/second (m/s). Solve the first three problems again, by first converting the given times, distances, and speeds into seconds, meters, and m/s. Give your answers in these units as well. Physics 1020.90 Lab Homework 1/19/11 Spring ‘11 Book Homework – use your textbook to help you answer these questions. 1. Define speed. 2. What does it mean when we say that speed is relative? Give an example from every-day life in which we encounter relative speeds. 3. What are average and instantaneous speeds? What are the equations that define them? While driving, in what instance(s) might average and instantaneous speeds be the same? In what instance(s) might they be different? 4. What is the difference between the terms speed and velocity? Can two cars have the same speed, but different velocities? Could they have the same velocity but different speeds? If so, give an example of how. 5. What is acceleration? What is the equation for acceleration? What are three distinct ways in which a car may experience acceleration? (Or, three ways in which a car can be accelerating?) 6. The gas pedal of a car is sometimes referred to as “the accelerator”. This re-enforces what common misperception about acceleration? In light of your answer to the previous question, how many other “accelerators” does your car have?