PHYS 201 TEST
#2 10/09/09 DR. HOLMES NAME
Do all seven problems. The worth of each part of each problem is marked beside the place for the answer. Show your work for partial credit. SET EACH PROBLEM UP FIRST. Do the algebra only if you have time. All numerical answers should be in MKS units unless otherwise indicated. Work should be under the problem, or clearly labeled on an extra sheet placed underneath the top page of the test.
INFORMATION: MASS OF EARTH = 6.0 x 1024kg; RADIUS OF EARTH = 6,380 km.
1. A ball of mass 0.4 kg is thrown from the top of a building 15 meters high (above the ground) with an initial speed of 27 m/s at an angle of 33° above the horizontal. The object then hits the ground (assume a level surface and assume no air resistance).
a) How far away from the building (where the person threw it, horizontal distance) does the object land?
86.2 m.
b) How long a time is the object in the air?
3.80 sec.
c) Draw a picture of the situation, and include on the picture all the given information in the problem:
2. A centrifuge spins objects around in a circle of radius = 22 cm. For parts a, b, c and d, assume the frequency of rotation is 4,000 rpm (revolutions per minute).
a) What is the frequency in cps (cycles per second)?
66.67 cycles/sec.
b) What is the tangential speed (in m/s) of an object in the centrifuge due to the spinning motion?
92.15 m/s.
c) What is the magnitude of the acceleration of an object due to the spinning?
38,601 m/s2.
d) What is the direction of that acceleration [toward the center, toward the outside, along the direction of motion, opposite the direction of motion, or other]?
Toward the center.
e) At what frequency would the centrifuge have to spin (either in cps or rpm) if the resulting acceleration were to equal 50 times the acceleration due to gravity (a = 490 m/s2)?
7.5 cps = 451 rpm.
3. A boat can travel at a speed of 4 m/sec on a calm lake. This boat is now put in a river that flows downstream at a rate of 3 m/sec.
a) What direction should a pilot point the boat to go directly across this river? [Indicate an angle measured from straight across, and indicate whether the angle is directed upstream or downstream.)
48.6o upstream.
b) How long will it take if the river is 85 meters wide?
32.1 seconds.
c) What direction should the pilot head the boat to get across the river in the least time?
straight across.
d) How long will be the least time?
21.25 seconds.
4) An object rests on a scale inside an elevator.
a) What is the mass of an object on the scale if the scale reads 700 Nt. when the elevator is at rest?
71.43 kg
a) If the scale reads 750 Nts with the object of part a on the scale at a later time (some time later - not just after it was at rest), is the elevator moving: [up; down; none - zero speed; can't be determined from information given]?
can't be determined from information given.
c) If the elevator (sometime later, not just after it was at rest) has the scale reading 620 Nts (as in part b), is the direction of the acceleration: [up; down; none - zero acceleration; or can't be determined from information given] ?
Up.
d) If the scale reads 750 Nts. (with the same object on the scale in the elevator as in part a above), what is the value of the acceleration of the elevator?
+0.70 m/s2 .
5) A 50 kg satellite is to be put into orbit around Triton, a moon of
a) What will the period of orbit of this satellite be?
9,662 sec = 161 minutes.
b) What speed should this satellite have in order to orbit with a circular orbit at this radius with this period?
975 m/s = 2,184 mph.
c) What is the force of gravity due to Triton on the satellite while it orbits at this radius?
31.7 Nt.
6) Consider a weight hung from a combination of a rod attached to the left wall and a rope attached to the ceiling. The angle the left rope makes with the ceiling is 75o and it is attached to the right (far) side of the rod so the rope is angled to the left as it meets the rod, and the angle the rod makes with the left wall is 55o. The weight is 150 Nt.
a) Does the rod push up and to the right, or down and to the left?
Down and to the left.
b) What is the magnitude of the force of the rod?
60.4 Nt..
c) What is the tension in the rope?
191.2 Nt.
7) Two people carry a weight of 650 Nt on a board of length 220 cm, one person lifting on the left and one on the right. The weight is located 180 cm from the left end of a board. The weight of the board can be neglected.
a) Is the left force, Fleft: [ less than; the same as; or greater than] the weight, W ?
less than
b) Is the left force, Fleft : [ less than; the same as; or greater than] the right force, Fright ?
less than
c) What is the magnitude of the left force, Fleft ?
118.2 Nt.