Practice test 2

Practice test 2
Momentum and impulse
p = mv, F = ∆p /∆t, I = ∆p = F∆t.
Center of mass: xCM = ∑mixi/M, yCM = ∑miyi/M, zCM = ∑mizi/M, M = ∑mi.
Rotations
ωavg = (θf - θi)/(tf - ti) = Δθ/Δt.
ωf = ωi + α(tf - ti), θf = θi + ωi(tf – ti) + ½α(tf – ti)2,
τ = r × F = Iα = ΔL/Δt, L = Iω.
Moment of inertia: I = ∑miri2.
Rolling: KEtot = (1/2)mv2 + (1/2)Iω2, v = rω.
Ideal Fluids
Equation of continuity: A1v1 = A2v2
Bernoulli’s equation: P1 + ρgh1 + ½ρv12 = P2 + ρgh2 + ½ρv22
Viscous fluids
Poiseuille’s law: Q = π∆Pr4/(8ηL)
Stokes' law: F = 6πηrv
Reynolds number: R = ρDv/η
Surface tension, Laplace's law for a spherical membrane: Pi - Po = 2γ/r.
Capillary action: h = 2γcosθ/(ρgr).
QUESTION 1
Which of the following statements is false?
a. An aneurysm in an artery leads to a locally elevated blood pressure.
b. Plaque deposit on an artery or arteriole wall leads to a decreased local blood pressure.
c. Plaque deposit on an artery or arteriole wall can lead to the collapse of that vessel.
d. Plaque deposit on an artery or arteriole wall causes an increase in local blood pressure and can lead to
bursting of that vessel.
e. The speed of the blood increases as it moves through a region of an artery with plaque deposit.
QUESTION 2
A fan rotating with an initial angular velocity of 1000 rev/min is switched off. In 2 seconds, the angular
velocity decreases to 200 rev/min. Assuming the angular acceleration is constant, how many revolutions
does the blade undergo during this time?
a. 20
b. 10
c. 100
d. 125
e. 1200
QUESTION 3
A constant horizontal force of 10 N is then applied on the block over a distance of 4 m. (That is, the force is
applied on the initially stationary block, and the block accelerates. After the block has moved 4 m,
application of the force ceases.)
After the application of the horizontal force, what is the magnitude of the momentum of the block?
a. 40 kg m/s
b. 80 kg m/s
c. 160 kg m/s
d. Not enough information given to answer the question.
QUESTION 4
The onset of turbulent flow happens for a Reynolds number of about
a. 0.
b. 2300.
c. 5200.
d. 100000.
e. infinity.
QUESTION 5
A 5.00 kg mass sliding along a horizontal frictionless surface at 2.00 m/s collides with a 1.00 kg stationary
mass. After the collision the two masses stick together and contact a light Hooke's-law spring with spring
constant k = 1000 N/m. What is the maximum compression (in m) of the spring?
a. 0.016 m
b. 0.02 m
c. 0.01 m
d. 0.14 m
e. 0.13 m
QUESTION 6
A spherical balloon is filled with air to a radius of 10 cm. Use Laplace's law to find its surface tension
assuming the pressure inside is 5 kPa higher than the pressure outside.
a. 10000 N/m
b. 1000 N/m
c. 2500 N/m
d. 250 N/m
e. 5000 N/m
QUESTION 7
Which has the greatest effect on the flow of fluid through a pipe? That is, if you made a 10% change in
each of the quantities below, which would cause the greatest change in the flow rate?
a. the fluid viscosity
b. the pressure difference
c. the radius of the pipe
d. the length of the pipe
e. the material the pipe is made of
QUESTION 8
Two blocks of mass M and 3 M are placed on a horizontal frictionless surface. A light spring is attached to
one of them, and the blocks are pushed together with the spring between them. A cord holding them
together is burned, after which the block of mass 3 M moves to the right with a speed of 5 m/s. What is the
speed of the block of mass M?
a. 15 m/s to the right
b. 1/3 m/s to the left
c. 1/3 m/s to the right
d. 15 m/s to the left
e. 5/3 m/s to the left
QUESTION 9
A DVD is rotating with an ever increasing speed. How do the angular velocity, angular acceleration,
tangential velocity, and tangential acceleration compare at points P and Q?
a. Points P and Q have the same angular velocity but point Q has a larger angular acceleration.
b. Points P and Q have the same angular velocity and the same angular acceleration.
c. Point Q has a larger tangential acceleration but points P and Q have the same tangential velocity.
d. Points P and Q have the same tangential velocity and the same tangential acceleration.
e. Angular velocity, angular acceleration, tangential velocity, and tangential acceleration are larger for
QUESTION 10
A skater who is spinning and throws her arms out slows down because
a. she makes her rotational mass or moment of inertia smaller.
b. she makes her rotational mass or moment of inertia bigger.
c. she increases friction.
d. she exerts less torque.
QUESTION 11
The shape of a droplet of liquid on a surface is due to a combination of
a. adhesion and cohesion.
b. capillary action and pressure.
c. capillary action and gravity.
d. pressure and cohesion.
e. capillary action and adhesion,
QUESTION 12
One end of a M = 0.1 kg meter stick is attached to a wall, and provided with a pivot. A vertical force F is
applied to the other end to make the net torque about the pivot point zero. What is the magnitude of F and
the direction of the torque produced by F.
a. F = 1 N, torque = 1 Nm upward.
b. F = 0.1 N, torque = 0.2 Nm out of page.
c. F = 0.5 N, torque = 0.5 Nm into the page.
d. F = 0.1 N, torque = 0.1 Nm out of page.
e. F = 0.5 N, torque = 0.5 Nm out of page.
QUESTION 13
A 104 N car is lifted by a manually operated hydraulic lift. The area of the shaft of the lift is 80 cm2; the
area of the piston that forces liquid into the system is 2 cm2. What minimum force must be exerted on this
piston to lift the car?
a. 5000 N
b. 125 N
c. 62.5 N
d. 104 N
e. 250 N
QUESTION 14
A 2kg block of wood is floating in water. What is the magnitude of the buoyant force acting on the block?
a. It cannot be determined since we do not know the density of the wood.
b. 2 kg
c. 0
d. 19.6 N
e. 2000 N
QUESTION 15
The radius of the aorta is ~ 10 mm = 10-2 m and the blood flowing through it has a speed ~ 300 mm/s = 0.3
m/s. A capillary has a radius ~ 4×10-3 mm = 4×10-6 m, but there are literally billions of them. The average
speed of blood through the capillaries is ~ 5×10-4 m/s.
(i) Calculate the effective cross sectional area of the capillaries and
(ii) the approximate number of capillaries.
a. (i) 0.06 m2, (ii) 1.2*109
b. (i) 0.188 m2, (ii) 3.75*106
c. (i) 0.06 m2, (ii) 3.75*1010
d. (i) 0.3 m2, (ii) 4*106
e. (i) 0.188 m2, (ii) 3.75*109
QUESTION 16
Your shopping cart is moving without friction with constant velocity down an aisle in the grocery store.
You drop a large can of beef stew straight down into the cart.
a. The cart slows down because its momentum is distributed over a larger mass.
b. The cart retains exactly the same velocity, because only its mass has increased.
c. The cart speeds up because its mass has increased.
d. The cart speeds up because its momentum has increased.
e. The cart retains exactly the same velocity, because velocity is conserved.
QUESTION 17
A 40 kg child standing on a frozen pond throws a 0.5 kg stone to the east with a speed of 5 m/s. Neglecting
friction between the child and the ice, what is the recoil velocity of the child?
a. 5 m/s west
b. 5 m/s east
c. 0.25 m/s west
d. 0.0625 m/s west
e. 0.0125 m/s east