PHY 211 Laboratory for 11/18/03

Exam III

Exam III will take place during the lab period on Tuesday, November 18. As before, you will have the full three hours. The exam will consist of 6 to 8 problems and cover Chapter 7.4 (centripetal acceleration) through Chapter 10. We will cover Ch 10 problems with a tutorial during Friday's lecture period. Catch up on the homework problems and come prepared with questions!

Below are a few sample problems from a previous exam. You are responsible for all material covered in lecture and homework assignments. DO NOT ASSUME that a subject not covered in the sample exam below will not show up on the exam! As usual, you will be provided with an equation sheet.

(NOTE: I haven't double checked the arithmetic for the answers. Please let me know if you get something different.)

Sample Physics 211 Exam III

  1. A fully suited 100 kg astronaut stands on a spherical astroid of diameter 1.0 km and mass 2.5 x 1012 kg.
    a) What is the astronaut's "weight" on this asteroid?
    b) With what speed must she jump to escape the asteroid?

    F = Gm1m2/r2 where r = 500 m yields F = .0667 N. Vesc = sqrt(2GM/r) = .82 m/s

  2. A uniform 2.0 m wide, 30 lb sign is supported at the upper left corner by the wall and by a wire at 37o at the other corner. Find the tension in the wire and the horizontal and vertical forces exerted by the wall.

    Place a vertical and horizontal force acting from the wall. Torques about the wall give (30 lb)(1m) - (T)(2m)sin37 = 0 --> T = 25lb. Torques about the where the wire attaches to the sign give -(30lb)(1m) + Fv(2m) --> Fv = 15lb. Finally, sum of forces gives Fh - Tcos37 = 0 --> Fh = 20 lb

  3. A child pushes a merry-go-round (MGR) with a tangential force of 100N. The MGR is a disc of mass 100 kg and radius 1.5 meters. Find its angular acceleration.

    t = I a --> (1.5m)(100N) = (1/2 (100kg)(1.5m)2 a --> a = 1.33r/s

  4. A 6 kg bowling ball of radius 12 cm with initial speed 10 m/s rolls without slipping up a 10o incline. How far along the incline will it roll before coming to a stop? (The moment of inertia for a sphere is 2/5MR2.)

    1/2mv2 + 1/2 (2/5mR2)w2 = mgh. Use w = v/R. Solve for h = 7.14 m, dsin10 - h --> d = 41 m up the incline.

  5. The inside of an underwater research station is maintained at atmospheric pressure. What net force acts on the 10m by 5m roof which is 8m below the sea surface?

    F = PA = rghA = 3.92 x 106N.

  6. A giant piece of styrofoam has dimensions 1.0.m x 2.0 m x .5 m and weighs 200N. How many 70 kg students can balance on top as it floats in the sea?

    FB = rVg = (1030)(1x2x.5)(9.8) = weight of students + 200N. weight of students = 9,900 N, m = 1000 kg, divde by 70 kg to get 14.4 --> 14 students.

  7. The maximum water flow from your faucet should fill a 1 L bottle in 10 sec.
    a) If the faucet has radius 1 cm, what flow velocity is required?
    b) What must be the minimum gauge pressure in the mainpipe which has radius 4 cm and is located 2 m below the faucet during maximum flow at the faucet?

    Av = flowrate --> pi(.01)2v = .001m3/10 sec -- > v = .32 m/s. Use Bernoulli's for part b ... Need v2 from A1v1 = A2v2 --> v2 = 1/16(v1) = .02m/s, so p1 + 1/2r.322 + rg(0) = p2 + 1/2r.022 + rg(-2m) -- > P2 - P1 = 19700 Pa.

  8. You are designing a Hg thermometer that will use the full 1.0 m height of a cylindrical tube for a temperature range of 100oC. If the reservoir bulb has volume 1 cm3, what should be the inner radius of the tube into which the Hg expands? For a 5 pt bonus, account for the expansion of the glass bulb. (bHg = 182 x 10-6 /oC and aglass = 3.2 x 10-6 /oC )

    DVHg = bHgVDT = pi(r2)L (-3aglassDT for bonus), --> r = .00761 cm without the glass correction and .00741 with it.

  9. How many molecules are there in a typical 1 L lungfull of air on a typical day at sea level? State what values you decide to use.

    PV = nRT --> (100,000Pa)(.001m3) = n(8.314)(~300K) --. n ~ .04 moles.