Physics 1401
Exam No. 3
Physics 1401 Test 3
Name______________
Instructions: Show all your work and make sure I can find your answers. Best of luck.
Multiple Choice (Show all work for partial credit):
1. A certain wheel has a rotational inertia of 12 kg · m2. As it turns through
5.0 rev its angular velocity increases from 5.0 rad/s to 6.0 rad/s. If the net
torque is constant its value is:
a.) 0.016 N · m
b.) 0.18 N · m
c.) 0.57 N · m
d.) 2.1 N · m
e.) 3.6 N · m
2. An 80-kg man balances the boy on a teeter-totter as shown.
The mass of the board 5 kg.
What is the approximate mass of the boy?
a.) 10 kg
b.) 20 kg
bo y
man
c.) 14 kg
fulcrum
4m
1m
d.) 45 kg
e.) 18 kg
3.) An ice skater with rotational inertia I0 is spinning with angular speed ω0. She pulls
her arms in, thereby increasing her angular speed to 4ω0. Her rotational inertia is then:
a.) I0
b.) I0/2
c.) 2I0
d.) I0/4
e.) 4I0
.
4. Three identical balls, with masses of M , 2M , and 3M , are fastened to a
massless rod of length L as shown. The rotational inertia about the left end of the
rod is:
a.) M L2/2
b.) M L2
c.) 3M L2/2
d.) 6M L2
e.) 3M L2/4
5.) A merry-go-round has a radius of R = 2.0m and a moment of inertia of I = 250kg.m2
and is rotating at 10 rev/s when a 30kg child drops onto its edge. What is the new
angular speed of the merry-go-round? Treat the child as a point particle.
a.) 12 rev/s
b.) 7.14 rev/s
c.) 6.76 rev/s
d.) 2.34 rev/s
6.) A thermometer indicates 98.6◦ C. It may be:
a.) outdoors on a cold day
b.) in a comfortable room
c.) in a cup of hot tea
d.) in a normal person’s mouth
e.) in liquid air
7.) A ball floats in a fluid with density of  = 1.35g/cm3 with half of its volume under
the fluid. If the ball has a radius of 6cm find the mass of the ball. Vol of sphere =
(4/3)R3
a.) 32 gm
b.) 13.29 gm
c.) 150.66 gm
d.) 610.7 gm
8.) A large water tank (water density = 1000 kg/m3 ), open at the top, has a small hole in
the bottom. When the water level is 30 m above the bottom of the tank, the speed of the
water leaking from the hole:
a.) is 2.5 m/s
b.) is 24 m/s
c.) is 44 m/s
d.) cannot be calculated unless the area of the hole is given
e.) cannot be calculated unless the areas of the hole and tank are given
9.) A hydraulic press has one piston of diameter 2.0 cm and the other piston
of diameter 8.0cm. What force must be applied to the smaller piston to
obtain a force of 1600N at the larger piston?
a.) 6.25 N
b.) 25 N
c.) 100 N
d.) 400N
e.) 1600 N
10.) The specific heat of lead is 0.030 cal/g · C◦. 300 g of lead shot at 100◦ C is mixed with
100 g of water at 70◦ C in an insulated container. The final temperature of the mixture is:
a.) 100◦ C
b.) 85.5◦ C
c.) 79.5◦ C
d.) 74.5◦ C
e.) 72.5◦ C
Short Answer…
11.) Explain why water’s unusual density properties between 0o– 4oC are probably a key
factor in the development of life on earth.
12.) Explain why the balancing wine holder doesn’t fall over (it is not being supported
on the right). It must be in equilibrium but this is what is called an unstable equilibrium.
Show that the center of mass of the system must be directly over the point of support on
the ground and that if the center of mass is moved to either side the bottle will fall over.
You will need to draw a couple of diagrams.
Show all Work
13.) A helium (He = 0.179 kg/m3) filled balloon is spherical with a radius of 0.40m and
has a deflated mass of 0.25kg. The density of air is 1.29 kg/m3. Find the acceleration
with which the balloon rises when released.
14.) A 1200N boom is supported by a cable connected to the wall. The boom is hinged
on the bottom and a 2000N weight hangs from its end.
a.) Find the tension in the support cable.
b.) Find the forces on the hinge at the ground.
15.) The pulley has a mass of M = 5kg and radius R = 2m, m = 2kg and starts 5m above
the ground. There is no friction.
a.) Find the acceleration of the system.
b.) How fast is the 2kg mass going when it reaches the ground?