Physics 213 Test 2 PPAM (Problems Priced asmarked)Oct 13, 1999

Warm-ups, 5 points each.

1. What is the law of conservation of energy?

2. What is the work-energy theorem?

3. Define power.

4. What must always be the positive direction in a circular motion problem and why?

5. What is the direction of the net force on an object that is moving in a circular path?

Use the figure below for problems 6 thru 9.

6. If the pulling force P is 150 N and the crate doesn't move, what is the magnitude of friction force f?

7. If the pulling force P is 200 N and the crate doesn't move, what is the magnitude of friction force f?

8. If the force of sliding friction is 250 N, what force is necessary to keep the crate sliding at constant velocity?

9. If the mass of the crate is 50 kg and sliding friction is 250 N, what is the acceleration of the crate when
the pulling force is 250 N?________ 300 N? _________ 500 N?________ Applications: 10 points each

10.The famous Daredevil Gazelle Gi-Gi is going to demonstrate just how precise she can jump by playing Gi-Gi basketball. She is going to leap from the floor and into a large basket attached to the wall of the stadium. Actually, all she can do well is control her speed and angle of take off. She relies on her staff physicst to decide the location of take off and landing. If she is to take off from a point 80 meters from the wall, at a speed of 60 m/s and an angle of 53° , at what height on the wall should the basket be placed for her landing?

11. A girl is pulling a 5 kg block up a hill by pulling on it with a horizontal force of 100 N as indicated in the figure. Find the acceleration of the block.

12. What does each of the scales read in the picture below ?

13. A 500 kg cart, including the passengers, is initially at rest. When the srping is compressed, the cart is launched for a trip around the loop-the-loop whose radius is 10 m. If the spring constant is 68,000 N/M, determine the distance z the spring must be compressed in order for the speed of the cart at the top of the loop to be 12 m/s ? Ignore friction, and use g = 10 m/s2 .

14. A truck initially at rest at the top of a hill is allowed to roll down without friction. At the bottom its speed is 4 m/s. Next, the truck is again rolled down the hill without friction, but this time it does not start from rest. It has an initial speed of 3 m/s on top, even before it starts going down the hill. How fast is it going when it gets to the bottom?

1. 3 m/s

2. 4 m/s.

3. 5 m/s.

4. 6 m/s.

5. 7 m/s