PHY2053, Review
Dec 1st, 2013
Problem 1
●  Given the following vectors: ~ = 2x̂
B
~ = 1x̂ + 5ŷ
A
3ŷ
●  What is the value of the following expression?
~ B|
~
|A
●  Answer: 2.24 ~ + B|
~
|A
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 2
●  A large horn with fundamental frequency f0 = 500 Hz
is mounted on a car that is moving to the left at speed
V. An observer in another car is moving to the left at
speed 2V as shown in the figure. If the speed of
sound in the air is 343 m/s and V = 20 m/s, what
frequency does the observer hear? ●  Answer: 527.5 Hz
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 3
●  A uniform disk with mass M, radius R= 0.5 m, and
moment of inertia I = MR2/2 rolls without slipping
along the floor at 2 revolutions per second when it
encounters a long ramp angled upwards at 45° with
respect to the horizontal. How high above its original
level will the center of the disk get (in meters)?
●  Answer: 3.0 m
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 4
●  The ideal mechanical advantage is
defined to be the ratio of the weight W
to the force of the pull Fp for
equilibrium (i.e. W/Fp in equilibrium)
Assuming that the pulleys rotate without
friction and without the rope slipping,
what is the ideal mechanical advantage
of the combination of pulleys shown in
the figure?
●  Answer: 7
PHY2053,
Fall 2013, Review, Dec 1, 2013
Problem 5
●  At time t = 0s, a 2 kg object’s position and velocity
are
~r = (2m)x̂ + (3m)ŷ ~v = ( 6m/s)ŷ
●  It is subject ta force F~ = (8N)x̂, where x̂ and ŷ are
the unit vectors in the x and y-direction, respectively.
What are the magnitude of the angular momentum of
the particle about the origin and the magnitude of the
torque about the origin, respectively?
●  Answer: 24 kgm2/s; 24 Nm
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 6
●  What is the minimum radius (in m) that a spherical
helium balloon must have in order to lift a total mass
of m = 10kg (including the mass of the empty
balloon) off the ground? The density of helium and
air are ρHe= 0.18 kg/m3 and ρAir = 1.2 kg/m3,
respectively.
●  Answer: 1.33 m
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 7
●  Near the surface of the Earth, a startled armadillo
leaps vertically upward at time t = 0. At time t = 0.5 s
it is at a height of 0.98 m above the ground. At what
time does it land back on the ground?
●  Answer: 0.9 s
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 8
●  A thin stick with mass M, length L, and moment of
inertia ML2/3 is hinged at its lower end and allowed
to fall freely as shown in the figure. If its length L =
2m and it starts from rest at an angle θ = 20° , what
is the speed (in m/s) of the free end of the stick when
it hits the table?
●  Answer: 7.43 m/s
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 9
●  A 1kg beaker containing 2.0 kg of oil
(density = 916 kg/m3) rests on a
scale. A 2.0 kg block of iron (density
= 7860 kg/m3) is suspended from a
spring scale and is completely
submerged in the oil. Find the
equilibrium readings of both scales.
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 10
●  A puck has a mass of 0.129 kg.
Its original distance from the
center of rotation is 0.4 m and
it moves with a speed of 0.8 m/
s The string is pulled
downward 0.15m through the
hole in the frictionless table.
Determine the work done on
the puck.
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 11
●  A 2.0-kg block situated on a rough incline is connected to
a spring of negligible mass, having a spring constant of
100 N/m. The block is released from rest when the spring
is unstretched. The pulley is frictionless. The block moves
20.0 cm down the incline before coming to rest. Find the
coefficient of kinetic friction between block and incline.
PHY2053, Fall 2013, Review, Dec 1, 2013
Problem 12
●  What percentage of the volume
of an iceberg is above the
surface of the sea? The density
of sea water is 1024 kg/m3 and
the density of ice is 917 kg/m3.
●  Answer: ~ 10%
PHY2053, Fall 2013, Review, Dec 1, 2013