Physics 213 Test 2 PPAM (Problems Priced as marked)Oct 11, 2000

Warm-ups, 5 points each.

1. What is the law of conservation of energy?

2.

3. Define power.

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

Use the figure below for problems 5 thru 7.

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

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

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

8. A miner is pulled by a wagon of supplies to the top of a hill where he lives by hanging from a rope attached to the wagon. As the cart moves at increasing speed down the hill, the miner moves with increasing speed upward. Which is greater, T or his weight ? (You must draw a FBD to receive any credit.)

9. If a force F = (3i + 5j)N acts on a box of goodies over a displacement of x = (-2i + 5j) m, find the work done on the box by the force.

10. Ropes used in rock climbing are "springy" so they cushion a climber's fall. If the potential energy function for a given rope is given by U = k x² - bx , where x is the distance stretched, k = 5 J/m² and b = 3 J/m , find the force as a function of the distance stretched for this rope.

Applications: 10 points each

11.The famous Daredevil Gazelle Gi-Gi is giving a ballet performance on the deck of the USS OutThere aircraft carrier when she slips on a wet spot and slides horizontally off the deck at a speed of 60 m/s. If the deck is 80 meters above the water, how far does Gi-Gi have to swim to get back to the ship before the sharks get her?

12. A 5 kg block is set into motion up an inclined plane with an initial speed of 20 m/s. The block comes to rest after traveling 12 m up the incline, which is inclined at an angle of 37E with the horizontal.

Find the coefficient of kinetic friction between the block and the surface in the figure.

13. A 400 N kid rides a Ferris Wheel at the circus. She is sitting on a scales, to see how her weight (accrding to the scales ) varies as she goes around. The Ferris Wheel has a radius of 40 m and she is moving with a constant speed . If the strap holding her in the seat must exert a force of 100 N down to hold her in the seat at the top of the ride,
a) How fast is she moving? (You must draw a FBD to receive any credit.)

b) What does the scales read at the bottom of the of the Ferris Wheel? (You must draw a FBD to receive any credit.)

14. Determine the reading of each of the scales in the figure below. (hint: draw a FBD and sum the forces for each pulley and the block.)

15. A 5-kg penguin sits on top of a 10-kg sled, as in Figure below. A horizontal force of 45 N is applied to the sled, but the penguin attempts to impede the motion by holding onto a cord attached to a wall The coefficient of kinetic friction between the moving surfaces is 0.2.

(a) Draw the force diagram for the penguin and identify the Newton's third law reaction force for each force you include.

(b) Determine the tension in the string held by the penguin,

(c) Find the acceleration of the sled.
Bonus 10 points

The well-loved Mr. Nicholson was riding on the back of his miat. When all of the sudden, his excellent driver slams on her brakes! UNFORTUNATELY, he flies over the top of Carrie and Allison's heads (clearing the miat). He departs the top of the car at an angle of 37° at an astonishing speed of 80 m/s. How far did Nick fly before he landed on the street and was run over by a mack truck?