TEACHER'S TEACHERS'S TEACHER'S TEACHER'S
Ken Cheney
10/28/2005
5:04/C0
Physics 31A Final
1. SKIING
A 200 lb skier is going down a 23 degree slope, no friction. What
is the acceleration in ft/s/s?
32*SIN(23)
a. 4.57, *b. 12.5, c. 20, d. 30.8, e. 42
2. MONKEY
A monkey 23 m up a tree throws a coconut down at you with a
velocity of 13 m/s. How many seconds do you have to jump?
(-13+SQR(13*13+2*23*9.8))/9.8
a. -6.21, *b. 1.21, c. 1.89, d. 5.77, e. 8.91
3. BURNING MINE SHAFT
You are climbing up a burning mine shaft using a weak old rope. If
you weigh 230 newtons and the rope can support 230+16 newtons, what is
your maximum acceleration, in m/s/s?
9.8*16/230
a. 1.07, b. 2.23, *c. .682, d. 10.5, e. .0696
4. DURIVE CENTRFICAL ACCELERATION
Durive centrifical acceleration any way you want. Explain lots!
5. GLIDER LAUNCHER
A 40 kg hang glider pilot plans to launch herself by compressing a
spring .81 m, k=400 Nt/m. The spring will accelerate her down a 37
degree frictionless slope to a level section 38 m vertically below her
starting point. She then travels across 12 m of level snow with a
coefficient of friction of .38. A short, frictionless ramp then
launches her straight up. How many meters will she rise above the
level section?
38-.38*12+400*.81*.81/40/9.8/2
*a. 33.8, b. 39, c. 70.2, d. 113, e. 135
6. SAFETY IN SCIENCE
A saw blade is to be stopped within 3.8 revolutions. If the
initial velocity is 4,300 RPM what angular acceleration is required (in
revolutions/sec squared)?
(4,300/60)**2/(2*3.8)
a. 269, b. 382, c. 513, *d. 676, e. 890
Physics 31A Final - Ken Cheney - V. 5:04/C COPY 0 PAGE 2
7. AUTO BRAKE
You are designing a brake to stop a saw blade within .76
revolutions after the motor is turned off. The initial speed is 1,200
revolutions per minute. The blade has a radius of .043m and a mass of
.26 kg. Find the torque required in nt m. I=m R R/2 for a uniform
disk.
.26*.043*.043*1,200*1,200*PIX(1)/(7200*.76)
*a. .397, b. .617, c. .775, d. 1.28, e. 1.47
8. ELEPHANT STOOL
A stool for a 56,000 N circus elephant is in the form of a cyinder
of .29 squar meters in area and 1.1 meters high. Young's modulus for
the stool is 2.4 E7 N square meter. How many meters does the stool
sink when the elephant sits on it?
56,000*1.1/.29/2.4 E7
a. .00173, b. .00342, c. .0059, *d. .00885, e. .158
9. PIPES
How many feet long should a pipe with one closed end and one open
end be so the harmonic just higher than the fundamental is 54 Hz?
Assume the velocity of sound is 1,100 f/s. SKETCH, EXPLAIN!!!
3*1,100/4/54
a. .0491, b. 25.5, c. 20.4, *d. 15.3, e. 10.2
10. THERMAL PENDULUM
What will be the % change in length of a pendulum of 1m original
length if the temperature changes by 24 C? The coeffecent of thermal
expansion is .000006 1/C. E-6 means ten to the -6 power.
24*.000006*100
*a. .0144, b. .0306, c. .351, d. .731, e. 1.08
11. EVERYTHING
You burn hydrogen and oxygen to make water, just the right ratio.
The final pressure is low enough so the water is all in the form of a
gas. If the temperature goes from 290 C to 1,800 C, the chamber bulges
enough to increase the volume 26%, and the initial pressure is .91
atmospheres, what is the final pressure?
2*.91*(1,800+273)/(3*(1+26/100)*(290+273))
a. 1.19, *b. 1.77, c. 2.5, d. 5.23, e. 6.72
12. RUNNING FORK
The teacher is moving away from you at 2.7 m/s. She is holding a
tuning fork of 760 Hz. What beat frequency do you hear between the
direct sound and the sound reflected from the board in front of the
teacher? The velocity of sound is 300 m/s.
760*2*2.7/300
a. 1.42, b. 6.53, c. 11, *d. 13.7, e. 72
Physics 31A Final - Ken Cheney - V. 5:04/C COPY 0 PAGE 3
13. MERCURY LAKE
A lake of mercury is found on the moon. It is 560 cm deep. The
acceleration of gravity is 163 cm/sec. Density of mercury is 13.6
gm/cubic cm. You plan to drain the lake using a large pipe of area 9.1
square cm leaving the lake horizontally. This pipe then narrows to 3.8
square cm before emerging horizontally into a bottomless pit. To save
materals you want to make the pipes as thin as possible; therefore you
must know the pressure in the large pipe. What is the pressure, in
dynes/square cm?
13.6*163*560*(1-(3.8/9.1)**2)
*a. 1.02 E6, b. 1.11 E6, c. 2.09 E6, d. 3.18 E6, e. 4.11 E6
14. TO THE CENTER
You are standing 39 feet from the center of a massless turntable
which is rotating at .022 revolutions per second. If you try to walk
to the center of the turn table it will turn faster and faster till you
slip and slide off. How many feet from the center will you be when you
slip if your shoes have a coeffecent of friction of .36?
((.022*PIX(2)*39*39)**2/.36/32)**(1/3)
a. 4.44, b. 6.43, c. 10, d. 12.3, *e. 15.7