Monday 1 Nov:

Free Response Quiz:

1. A boat (500kg) is floating with 70% of its volume underwater.

Find:

                              i.      Density of boat

                             ii.      F_buoyancy

                            iii.      Mass of Water displaced

a.  70⁰ submerged means that object is 70⁰ as dense as water.

b. F_buoyancy = W_obj = mg        (for floating objects)

     à (500)(10) = 5,000N

c. m_water = m_obj             (for floating objects)

   à i.e., 500kg

 2. A rock lies at the bottom of a lake. Its volume is 3.0x10⁴ cm³.

 To lift it, it requires a 290N force.

a.      mass of water displaced

b.      mass of the rock

c.      density of rock

a.  r_water = m/v

    1000 = m / .03m³

     m = 30kg

b. W_rock =  F_{buoyancy +} F_lift

                W_rock = (mg)  + 290

                W_rock = 300  + 290 = 590N

                 M_rock = w/g = 590/10 = 59kg   

c. r_rock = m/v à 59/.03 = 1,967 kg/m³

                        Pascal’s principle:

http://webphysics.davidson.edu/physlet_resources/bu_semester1/c23_pressure_pascal.html

                        Archimedes’ principle:

http://www.onr.navy.mil/focus/blowballast/sub/work2.htm

http://www.hazelwood.k12.mo.us/~grichert/explore/dswmedia/floatlog.htm

3. Two banks (5m high) border a stream channel.

A 35m rope is attached directly in the middle of

the channel and a person swings from one bank

to the other. Find:

  a. Period       

  b. Time to swing across to other bank

c.  If banks were 15m high or 1m high, how would

the time to swing across be affected?

a. T = 2√ L

                T = 2√ 35

         T =  11.8 s

b. Time of ½ cycle = 11.8/2 = 5.9s

c. No!   It makes no difference, period (T) is not affected by starting height (or by mass). Only by length + gravity.

4. A water tank is 50m above a pipe that has a hole in it.

What is the speed of the water as it leaves the pipe?

KE = PE

1/2mv² = mgh

v = √2(10)(50)

v = 31.6m/s

5. A pipe has fluid moving rapidly through it and fluid

on the outside the walls of pipe. What will happen if

small holes are put in the pipe while the inside fluid is moving?

High velocity, low pressure.

 The outside fluid will be pulled/drawn in to the inside because of lower pressure inside than outside.

Work on free response (Quiz Wed):