Directions: Each problem is worth 5 points – 1 point for writing given information, 3 points for writing equations used and steps in the calculation, and 1 point for the correct answer (with units).
1.) In the next 30.0 s, the Earth will travel roughly 885 km (i.e. 550 miles) along its orbit around the Sun. Compute its average orbital speed in km/s.
2.) A baseball is thrown and in 2.0 s its shadow on the ground travels 180 m in a straight line. What’s the average speed of the shadow? Is that more, less, or the same as the average speed of the ball? Explain.
3.) Hair grows at an average rate of 3 x 10 -9 m/s. How long will it take to grow a 10 cm strand?
4.) Having traveled 900 km in 9.00 h, how fast should a driver go if he is to finish the entire 1000 km journet at an average speed of 100 km/h?
5.) A driver covered 42.0 km in 6.0 h (during that time she stopped for 30.0 min for lunch). She then speeds up, traversing another 56.0 km in 4.0 h. What was her average speed for the entire journey? What was her average speed while actually driving?
6.) The “Racing Roadsters” come roaring onto a highway at 100 km/h headed for the finish line 300 km away.
Their rivals, the “Screamin’ Demons,” are in hot pursuit and they arrive at the highway entrance one-half hour later. What must be their minimum average speed if they are to intercept the Roadsters this side of the finish line?
7.) Having traveled halfway to the end of a journey at an average speed of 15 km/h, how fast must you traverse the rest of the trip in order to average 20 km/h?
8.) A swimmer crosses a channel at an average speed of 10 km/h and returns at half that rate. What was his overall average speed for the round trip? [Hint: Let L be the one-way distance. Write expressions for the time-out
and time-back. The overall average speed is 2L divided by the total time.]
9.) To test a small rocket motor it’s fired up a long vertical tube. It rises to a height of 100 m in 5.0 s and then falls back to the ground at an average speed of 10.0 m/s. How long did the whole trip take, and what was the net average speed?
10.) A three-lap relay race is run at an average speeds for each lap of 10 km/h, 12 km/h, and 14 km/h. What is the average speed for the entire race? Guess at the answer and then calculate it.