Physics 213 Test 1 12 points each Sept. 15, 1999

1. In one of the homework problems you had a ball that moved from x = 0 at t = 0 to strike a wall 12 m away in 4 seconds, then return to its original location in another 4 seconds.

a. What was its displacement ?

b. What was its average velocity ?

c. What was its average speed?

2. Draw a motion diagram of an object that has:

a. negative velocity and positive acceleration.

b. constant acceleration and zero displacement over a some time interval.

3. For the velocity vs time curve below:

a. Find the total displacement traveled in 8 seconds by the object with this velocity vs time curve.

b. Find the total distance traveled in 8 seconds by the object with this velocity vs time curve.

4. Draw the acceleration vs time and displacement vs time (assume the object starts at the origin ) graphs for the object with the following velocity vs time graph.

For the first two problems 5 a and 5b below, Do not solve the problem. But for problem 6, also solve the problem:

Draw picture

Draw reference frame

Draw motion diagrams for each object over each time interval (if different) to determine signs for velocities and accelerations.

Indicate with A, B, C, etc, the pertinent events.

Write down x, v, and t values for each object at each of these positions, and acceleration between them.

5a. A metro train in Washington, D.C., starts from rest and accelerates at 2.0 m/s2 for 12 s. The train travels at a constant speed for 65 s. The speed of the train then decreases for 25 s until it comes to a stop. What is the total distance between stops?

5b. Bobby drops a brick off the bridge. Susie standing under the bridge, starts a stop watch when she sees the brick leave Bobby's hand. She stops the watch when the brick hits the water, noticing it takes the brick 4 seconds to reach the water. How high is the bridge above the water?

6. Martha is riding in a hot air balloon, rising at a constant 5 m/s. George watches nervously from the ground. At 30 m according to her altimeter, she releases a bouquet of flowers for George to catch. How long does it take the flowers to reach George?

7. Given the two vectors below, draw the vector:

a) A + B

b) A - B

8. a. What is the angular velocity in radians / second of the minute hand of a clock ?

b. A car is travelling on a curve of radius 100 m. Find its speed if it's centripetal acceleration is 20 m/s2 .

10 Points Bonus

George finally got up the courage to go hot air ballooning. He took his stuffed teaddy bear named Harry. (George never goes anywhere without Harry). The balloon is ascending at a constant rate of 20 m/s. But as he was dangling Harry over the edge of the gondola, showing him all the sights, Geoge accidentally dropped Harry. Trying to calm himself down, he measured the time it took Harry to splatter all over the pavement below. He noticed it was 10 seconds. (Ignore air resistance, use g = 10 m/s2). But at that same instant, grief -stricken George faints, and falls out of the gondola. Two seconds later the cold air striking him in the face wakes George up. How long does George have to prepare himself for death, after he wakes up?