Physics 213 Test 2 10 Points Each October 13, 1998

1. An object moves in such a way as to produce the velocity vs. time graph below. If the object starts at the orgin:

a) At which of the lettered times is the object's displacement greatest?_______

b) At which of the lettered times is the object moving the fastest? ________

c) Is the object moving away from or toward the origin between times A and B? _____________

d) Describe the object's motion at time C.

2. 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.)

3. 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. If the Ferris Wheel has a radius of 40 m and she is moving with a constant speed of 20 m/s, what does the scales read when she is at :

a) the top of the Ferris Wheel? (You must draw a FBD to receive any credit.)

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

4. A 700 N football hopeful in the elevator is trying to see if he can gain weight by weighing himself while riding in an elevator. What acceleration in which direction must the elevator have in order for the scales to read 900 N? (You must draw a FBD to receive any credit.)

5. A 20 kg block slides down the plane. If it is pulled by a 50 N force its acceleration is 6 m/s2, what is the kinetic coefficient of friction? (You must draw a FBD to receive any credit.)

6. 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.)

7. Use the figure below for parts a thru d.

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

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

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

d. 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?________

8. How much work is done by force F = (4 i + 5 j ) N, over the displacement r = (8 i - 6j) m ?

9. If a 4000 kg spaceship travelling 20 m/s receives 6 x 105 J of work from a booster rocket to speed it up, what will be its final speed ?

10. The famous Daredevil Gazelle Gi-Gi has decided to try for a new gazelle distance record by being shot from a cannon. She has prepared for the severe force of landing for weeks by doing an astonishing 1000 jumping jacks a day! The cannon is fired from a platform that is 100 m off the ground. The cannon is supposed to be aimed at an angle of 30E above the horizontal. But the guy hired to man the cannon doesn't really know how to operate it very well, and has no common sense. He sets the dial on the declination axis to -30Ethinking the minus sign is just a dash, and doesn't even notice that the cannon is pointed down 30E below the horizontal instead of instead of up 30Eabove the horizontal. So, how far from the base of the tower does Gi-Gi land? By the way, is her velocity at impact greater, less than or the same as the velocity would have been if she'd been aimed up 30E above the horizontal as intended?

Bonus #1: 10 Pts.

A neighbor's child wants to go to the carnival to experience the wild rides. The neighbor is worried about safety because one of the rides looks dangerous. She knows that you have taken physics, and asks your advice. The ride in question has a 44.5 N chair which hangs freely from a 9.14 m long chain attached to a pivot on the top of a tall tower. When a child enters the ride, the chain hangs straight down. The child is then attached to the chair with a seat belt and a shoulder harness. When the ride starts up, the chair rotates about the tower once every 3 seconds. When you ask the operator, he says the ride is perfectly safe. He demonstrates this by sitting in the stationary chair. The chain creaks but holds and he weighs 890 N. Has the operator shown that this ride is safe for a 222.5 N child?

Bonus #2

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) 2 Points Bonus: Draw the force diagram for the penguin and identify the reaction force for each force you include.

(b) 2 more points Bonus: Determine the tension in the string held by the penguin,

(c) 2 more points Bonus: and the acceleration of the sled.