PHYS 2010             Sample Exam for CH's  7, 8, 9

1]     A 0.150 kg object tied to a string is whirled in a horizontal circle at a constant angular speed
of 3.50 revolutions/sec. The tension in the string is 75.0 N. What is the length of the string?

2]     A wheel of diameter 0.80 m is initially at rest. It is then rotated with a constant angular
acceleration of 5.0 rad/s2 for exactly 10 revolutions of the wheel. Determine both the angular
speed of the wheel and the tangential speed for a point on the edge of the wheel at the end
of the 10 revolutions.

1]     A 150 gm object tied to a string is whirled in a horizontal circle such that the tension in the
string is 75.0 N when the angular speed is 3.50 revolutions/sec. How many meters, s, does
the object travel in 5.00 seconds? [ NOTE s is the circumferential distance traveled around
the circle.]

3]     A uniform beam 3.00 meters long has a weight of 245 N. It is supported on its left end by a cable.
A 500 N weight is located on the beam a distance of 1.00 meter from the left end. You supply a
force to the right end of the beam so that the beam is in equilibrium in the horizontal position (see
sketch). What are the tension in the cable, T, and the upward force, F, you must apply to the beam?
{HINT : Apply the equilibrium condition for two different axis’ of rotation !!}

ANSWER: T = 456 N , F = 289 N

3]     A solid wood sphere floats in alcohol (r = 0.806 x 103 kg/m3) such that exactly one half of the
sphere is submerged in the fluid.
A} Find the density of the wood.

B} Give the name and define the principle involved in the solution of this problem.

4]      A concrete canoe must be constructed such that most of its volume is air to insure that it will float in
water.  Assume such a canoe can be approximated as a uniform solid cube with sides 2.0 meters in length.
When placed in water, the cube floats upright with its bottom 1.5 meters below the water surface.

A)    Find the average density for the concrete canoe.         ANS:    0.75 gm/cm^3

B)    Find the absolute pressure at the bottom of the canoe.       ANS:    1.16  x  10^5   Pa

3]         A uniform beam 4.00 meters long has a weight of  350 N.  It is supported at a point 1.00 meter from the right
end by a fulcrum.  A 500 N weight is located on the beam a distance of 1.00 meter from the left end.  You supply a force
directed at the right end of the beam so that the beam is in equilibrium in the horizontal position (see sketch).
Determine BOTH the force exerted by you on the right end AND the force exerted on the beam by the fulcrum.

ANS:     F =  1560 N       Fulcrum =   2200 N

M ultiple Choice

1. Consider a point on a bicycle wheel as the wheel turns about a fixed axis, neither speeding up nor slowing down. Compare the linear and angular accelerations of the point.
1. Both are zero.
2. Only the angular acceleration is zero.
3. Only the linear acceleration is zero.
4. Neither is zero.

2.  If the net torque applied to an object is zero, then that object will experience:
1. a constant angular velocity
2. an angular acceleration
3. a centripetal acceleration
4. no angular motion at all
3.   When an object undergoes circular motion, that motion is the result of a

a.  centrifugal force
b.  centripetal force
c.   outward pushing force
d.  no force is required for circular motion

4.   Water pressure is the greatest against the

a.  top of a submerged object
b.  bottom of a submerged object
c.  sides of a submerged object
d.  is the same for all surfaces
e.  none of the above

5.   The buoyant force on an object will have its smallest value when the object is

a.  only partly submerged
b.  completely submerged but near the surface
c.  completely submerged but near the bottom
d.  the force is the same whether it is partly or completely submerged

6.   You sit on one end of a seesaw and your classmate sits on the other.  You are a distance A from
the fulcrum and your classmate is a distance B from the fulcrum.   The lever arm distance for the
torque you exert on the fulcrum pivot point is

a)     A + B
b)     A - B
c)     A
d)     B
e)     (A+B)/2