Page 1

Gladys is doing a physics experiment in her car. She accelerates across an empty parking lot and then slams on the brakes. Measuring the width of one parking space and then counting parking spaces she is able to get the distances for acceleration and braking. With her stopwatch, she also measures time for acceleration.

Given: Gladys accelerates for a distance of 168 m in 11.0 s and then skids to a stop in 84 m. Gladys and her car together have a mass of 1200 kg.

Find: (a) What is the acceleration of the car when it is accelerating? [2.78 m/s²]

(b) What is the force acting on the car when it is skidding to a stop? [6.7 kN]

(c) What is the coefficient of friction between the tires and the pavement?[0.57]

Page 2

Gladys is doing another physics experiment. She spins a ball on a cord about her head.

Given:  The ball has a mass of 55 g and the tension in the cord is 5.39 N. The distance from the ball to the hand is 1.75 m.

Find: (a) What is the centripetal acceleration of the ball? [98 m/s²]

(b) What is the angular velocity of the ball? [7.48 s^-1 ] or [1.2 rev/s]

(c) What is the linear velocity of the ball? [13 m/s]

Page 3

Now it is Oscar who is doing a physics experiment. He lowers a sack of rocks into a deep lake behind his house.

Given:  The rocks weigh 100 N in air but, when 2 m under the surface of the lake, have an apparent weight of only 80 N. The lake is 15 m deep.

Find: (a) What is the volume of the rocks?[2.0x10^-3 m³]

(b) What is the density of the rocks?[5.1x10³ kg/m³]

(c) What would be the apparent weight of the rocks if they were lowered to almost the bottom of the lake? [80 N or Same!]

Page 4

(Based on 4-B12 and recycled from a practice exam with two  numbers changed and a part added)
 In San Francisco's Exploratorium, a beautiful mechanics exhibit, called the Giant Pendulum, features a huge concrete and steel pendulum bob attached by a strong cable to the ceiling. Visitors can accelerate this huge object with small forces applied by refrigerator magnets attached to strings. After little experimentation, you learn how hard you can pull on the string before the magnet comes loose from the bob. Another thing you can do is a static force experiment.

Given: The bob is supported by a cable 20 m long and is pulled 15 cm to the side by a horizontal string attached to a 250 g pocket knife. The string then goes upward and outward to your hand at an angle of 40^o measured to the horizontal.

Find (a) How much tension is in the part of the string going to your hand? [3.8 kN]

(b) How great is the tension in the horizontal part of the string going to the Giant Pendulum bob?
[2.9 kN]

(c) How massive is the Giant Pendulum bob? [40 kg]

Page 5

15-A3    A large research balloon whose volume is 400 m³ is to be filled with helium at atmospheric pressure. The helium is stored in cylinders of volume 0.05 m³ at a pressure of 20 atm. How many cylinders are required?

[400 cylinders] or [421 cylinders]

Page 6

Based on 17-88   In a research program to utilize the earth's heat for electric power generation, an exploratory hole is being drilled in Idaho to a depth (about 2000 m) where hot rocks are found.

Given: The rock temperature at that depth is 130^oC. The surface temperature is about 20^oC. A small power plant would produce  power at the rate of 100 MW

Find: (a) Calculate the maximum thermodynamic efficiency of such a generating plant. [27%]

(b) At half this efficiency for a real power plant, at what rate would heat energy need to be extracted from the ground?  [733 MW]