Physics 221 Exam 2
Blood and water have the same contact angle with glass. The density of blood is 5% higher than that of water. (ρblood = 1.05 ρwater) While you make your capillary action measurements you find that water rises in the same tube a factor 1.69 higher than a blood sample. The surface tension of water at the same temperature is 0.073 N/m. What is the surface tension of the blood sample?
.045 N/m
A 65 kg physics student is at rest on a 5 kg sled that also holds a chunk of ice with a mass of 1.5 kg. The student throws the ice horizontally with a speed of 10 m/s relative to the ground. If the sled slides over a frozen pond without friction, how fast (in m/s) are the sled and student traveling with respect to the ground after throwing the chunk of ice?
.214 m/s
Suppose the flow rate of blood in a coronary artery has been reduced to 0.717 times its normal value by plaque deposits, and that the pressure difference across the artery has not changes. By what factor has the radius of the artery been reduced, assuming no turbulence occurs? Enter a number with three digits behind the decimal point.
.92
A ball initially at rest is hit by a club. It is in contact with a club for 6.0*10-3 seconds. Just after the club loses contact with the ball, the ball's velocity is 2.0 m/s. If the ball's mass is 50 g, what is the magnitude of the impulse the club gives to the ball?
0.1 kg m/s
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.
(i) 0.188 m2, (ii) 3.75*10^9
A centrifuge in a medical laboratory rotates at an angular speed of 3600 rev/min. When switched off, it rotates 50 times before coming to rest. What is the constant angular acceleration of the centrifuge?
-226.2/s^2
For a smooth sphere with a 22 cm diameter thrown through air (air density of 1.25 kg/m3, air viscosity 1.83*10-5 Pa-s), what is the speed (in cm/s) when the Reynolds number is 3882? Enter a number with 1 digit behind the decimal point.
25.8
A block of wood of uniform density floats so that exactly 1⁄4 of its volume is underwater. What is the density of the block?
250 kg/m^3
A 1 kg rock is suspended by a massless string from one end of a meter stick at the 0 cm mark. What is the mass m suspended from the meter stick at the 75 cm mark if the system is balanced?
2 kg
Calculate the gauge pressure (in Pa) inside a soap bubble 2.5 cm in radius using the surface tension γ = 0.015 N/m for the solution. Enter a number with one digit behind the decimal point.
2.4
An object moves with constant speed in the clockwise direction along the circular path shown below. At the point indicated by the black dot, in which direction is the angular velocity vector ω pointing?
D
A certain pump can exert a negative gauge pressure of 23.6 kPa. It is used to suck a liquid out of a bucket up a thin pipe. A 10.6 m column of the liquid exerts a pressure of 100 kPa. To what maximum height ( in m) can the the liquid be sucked up the pipe by this pump? Enter a number with two digits behind the decimal point.
2.5
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?
20
The four things that affect the amount of water flowing through a hose are
water viscosity, hose length, inlet and outlet pressure difference, and hose diameter.
A boy has a mass of 30 kg. He is standing on an icy pond, when a "friend" throws a 2 kg ball at him with horizontal velocity of 8 m/s. If the boy catches the ball, how fast will he be moving?
0.5 m/s
Angular speed is measured in units of s-1, which is rad/s. How many degrees correspond to 1 radian?
1 rad = 57.3 degrees
When the body requires an increased blood flow rate in a particular organ or muscle, it can accomplish this by increasing the diameter of arterioles on that area. By what factor must the diameter of an arteriole increase to double the volume flow rate of blood, all other factors remaining the same?
1.19
Two fluids have the same contact angle with glass. The density of fluid 1 is larger than the density of fluid 2 . (ρ1 = 1.07 ρ2) The surface tension of fluid 1 is larger than that of fluid 2. (γ1 = 1.40 γ2) Find the ratio h1/h2 of the heights to which a liquid will rise through capillary action in the same capillary tube. Enter a number with 2 digits behing the decimal point.
1.31
Two particles of masses 2 g and 6 g are separated by a distance of 6 cm. The distance of their center of mass from the heavier particle is
1.5 cm
A water pump generates a constant flow Q, which is causing a turbulent spray (Reynolds number R = 3200) out of this cylindrical nozzle: You want to achieve laminar flow with a Reynolds number below 2000 by picking a different nozzle. Your nozzle should have a diameter
1.6 D or greater
This pocket watch is keeping perfect time. What is the angular speed ω of its minute hand in units of rad/s?
1.75*10-3 rad/s
A 500 N weight sits on the small piston of a hydraulic machine in equilibrium. The small piston has area 2.0 cm2. If the large piston has area 40 cm2, how much weight does the large piston support ?
10000N
A Venturi tube may be used as a fluid flow meter. If the fluid flow rate in m3/s is 1.8 * 10-3 and the radius R1 = 1.9 *10-2 m of the inlet tube is 3.1 times the radius R2 of the outlet tube, and the fluid is water (ρ = 1000 kg/m3), find the pressure difference P1 - P2 in units of kPa. Enter a number with one digit behind the decimal point.
115.1
An intravenous (IV) system is supplying saline solution to a patient at the rate of 0.12 cm3/s through a needle of radius 0.2 mm and length 5.43 cm. What gauge pressure (in Pa) is needed at the entrance of the needle to cause this flow? Assume that the viscosity of the saline solution to be the same as that of water, η = 1.0*10-3 Pa-s, and that the gauge pressure of the blood in the vein is 1500 Pa. Enter an integer.
11871
The lungs can exert a negative pressure, with respect to atmospheric pressure, of up to 1.3 kPa. To what height can you suck water through a straw?
13 cm
A ball (mass 0.40 kg) is initially moving to the left at 20 m/s. After hitting the wall, the ball is moving to the right at 20 m/s. What is the impulse of the ball receives during its collision with the wall?
16 kg m/s to the right
A ball initially at rest is hit by a club. It is in contact with a club for 6.0*10-3 seconds. Just after the club loses contact with the ball, the ball's velocity is 2.0 m/s. If the ball's mass is 50 g, what was the magnitude of the average net force acting on the ball while in contact with the club?
16.7 N
A wheel with moment of inertia 0.08 kgm2 rotates about a fixed axis. Its kinetic energy is 1137 J. What is ts angular speed ω in s-1? Enter an integer.
169.0000
The angular acceleration of a object with moment of inertia 23 kg m2 about an axis is α = 1.5 s-2. A force is applied a distance 0.20 m from the axis, making an angle θ = 78 degree with the lever arm. What is the magnitude of this force in N? Enter an integer.
176
A centrifuge starts from rest. Its angular acceleration α is constant for 10 s. Its final angular speed is ω = 282 revolutions per second. What is its angular acceleration α in units of s-2? Enter a number with one digit behind the decimal point
177.2
A 2 kg block of wood is floating in the water. What is the magnitude of the buoyant force acting on the block?
19.6 N
A bicycle's wheels have a radius of 33 cm. The bicycle is traveling at a speed of 6.5 m/s. What is the angular speed of the front tire?
19.7 rad/s
Let g = 9.8 m/s^2. A hydraulic system is used to lift a 92 kg motor in a garage. If the motor sits on a piston of area 0.29 m^2, and a force is applied to a piston of area 87 cm^2, what is the minimum force that must be applied to lift the motor in units of N? Enter a number with one digit behind the decimal point.
27
A 44 kg object is placed on a 145 cm^2 platform. What is the pressure the object exerts on the platform in N/m^2? Let g = 9.8 m/s^2. Enter an integer.
29738
The volume flow rate of water through a horizontal pipe is 1.6 m3/min. Determine the speed of flow (in m/s) at a point where the diameter of the pipe is 9.9 cm. Enter a number with two digits behind the decimal point.
3.46
Substance A has a density of 2.0 g/cm3 and substance B has a density of 3.0 g/cm3. In order to obtain equal masses of these two substances, the ratio VA/VB of the volume of A to the volume of B has to be equal to Hint:
3:2
Mercury has an unusually large surface tension γ = 0.465 N/m. Calculate the excess pressure inside a drop of mercury 4 mm in diameter.
465 Pa
A beaker containing 5.0 kg of water is on a weighing scale. A 0.8 kg block of metal that has density 8*103 kg/m3 that is attached to a string is lowered completely into water without touching the bottom. Assume that the beaker is massless, and water has density 103 kg/m3, and g = 10 m/s2. What is the reading on the scale?
51 N
A wheel starts from rest with constant angular acceleration α. It requires 3.4 s to make 47 revolutions. What is its angular acceleration α in s-2? Enter a number with one digit behind the decimal point.
51.1
A block of a plastic material floats in water with 63.3% of its volume under water. What is the density of the block in kg/m^3? Enter an integer.
633
A soap bubble with radius of 3.0 cm is floating in air. What is the pressure difference across the two surfaces of the bubble? The surface tension of soapy water is γ = 69 * 10-3 N/m.
9.2 N/m^2
A nozzle with a radius of 0.23 cm is attached to a garden hose with a radius of 1.41 cm. If the speed of the water in the hose is 2.50 m/s, what is the speed of the water in the nozzle in m/s? Enter a number with two digits behind the decimal point.
93.96
A steel bridge is built in several segments, each 20 m long. The gap between segments is 2 cm at 18 oC. What is the maximum temperature that the bridge can manage before buckling?
95 degrees Celsius
The moment of inertia of a meter stick of length L = 100 cm and mass m = 50 g about a perpendicular axis through its center is mL2/12. Two 56 g masses are attached to the stick, at 22 cm to either side of the center. What is the moment of inertia of the system in units of kg cm2 about the perpendicular axis through the center of the stick? Enter an integer.
96
Three forces labeled A, B, C are applied to a rod which pivots on an axis through its center. Which force produces the torque with the largest magnitude about this axis? Hint: magnitude: τ = r Fsinθ r = vector pointing from axis of rotation to point where force F is applied. θ = smallest angle between r and F.
A
Fluid is flowing from left to right through the pipe. Points A and B are at the same height, but the cross-sectional areas of the pipe differ. Points B and C are at different heights, but the cross-sectional areas are the same. Rank the pressures at the three points, from highest to lowest.
A, B, C
Consider three drinking glasses. All three have the same area base, and all three are filled to the same depth with water. Glass A is wider at the top than at the bottom, glass B is cylindrical and so holds less water than A. Glass C is narrower at the top than at the bottom, and so holds less water than B. Which glass has the greatest liquid pressure at the bottom?
All three have equal pressure at the bottom
The picture below shows 5 blocks. The blocks have equal volumes but different masses. The blocks are placed in an aquarium tank filled with water and blocks 2 and 5 come to rest as shown in the figure. Which answer is correct?
Block 3 will come to rest in the same position as block 5
Two objects, A and B, have the same volume and are completely submerged in a liquid, although A is deeper than B. Which object, if either, experiences the greater buoyant force?
Both objects experience the same buoyant force
A disk is spinning with angular velocity ω as shown. It begins to speed up. While it is speeding up, what are the (i) directions of its angular velocity ω (ii) and its angular acceleration α? Angular acceleration does not necessarily point in the direction of the angular velocity. For a fixed rotation axis, it points in the direction of ω if the rotation rate is increasing and opposite to the direction of ω if the rotation rate is decreasing.
C, C
Modeling a meter stick as a forearm, compare the force FB that the biceps has to exert to keep the forearm horizontal to the weight of the forearm FW = mg. Let d = 10 cm and the distance from where the biceps muscle attached to the center of mass be d' = 40 cm.
Fb= 5 mg
Referring to the graph below, which phase has the smallest specific heat capacity?
Gas
In soap box car races, the cars are boxes with wheels. They begin at rest at the top of a hill, and at the start of the race they all begin rolling down the hill. The soap box car that reaches the bottom of the hill first is the winner. You have entered a soap box car race where the rule is that all the wheels and cars must have equal mass. Since you have taken Physics, you know that it is worse to have wheels with spokes (where the mass is mostly on the rim) rather than solid wheels because
Given the same torque, the wheels with spokes have a higher rotational mass or moment of inertia and therefore will have a smaller angular acceleration.
Orange growers in Florida spray their trees with water when they expect a freeze. Why does this work?
If a mixed phase of water and ice is present, the temperature does not drop below 0 degrees C.
If the absolute temperature of a gas is halved, what happens to the average (root-mean-square or RMS) speed, √<v2>, of the gas molecules?
It decreases to 1/√2 the original average speed.
The fundamental dimensions of pressure are
M L^-1 T^-2
An ice-cube sits in a bath of water. The water, the ice and the surrounding air are all at 0 degrees C. Does heat enter the ice cube?
No
Which of the following statements are false?
Plaque deposit on an artery or arteriole wall causes an increase in local blood pressure and can lead to bursting of that vessel.
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?
Points P and Q have the same angular velocity and the same angular acceleration.
In a stationary homogeneous liquid near the surface of Earth, which of the following is true?
Pressure is the same at all points at the same height.
In the constellation Orion, you can easily observe the difference between the reddish looking star Betelgeuse and the bluish looking star Rigel. Which of the two has the hotter surface temperature?
Rigel
On a humid summer day, perspiration does not cool you off much. Why?
The air is almost saturated with water vapor and there is almost no net evaporation.
A chair has a wooden seat but metal legs. The chair legs feel colder to the touch than does the seat. Why?
The metal has a higher thermal conductivity than the wood.
True or False: A rotating body can be in one of the types of equilibrium.
True
Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest?
When it is 75 degrees Fahrenheit with 50% relative humidity.
Suppose you are on a cart, initially at rest on a frictionless, horizontal track. You throw a series of identical balls against a wall that is rigidly mounted to the cart. If the balls are thrown at a steady rate and bounce straight back, is the cart put into motion?
Yes, it starts to move to the left and steadily gains speed.
Suppose you work in the E.R. and a choking patient comes in with their trachea half obstructed. (The diameter is half of what it was before the obstruction.) You manage to correct the problem and send them on their way safely, explaining that such obstructions are particularly dangerous because
a half-blocked airway passes only 1/16 the regular amount of air.
Water with air bubbles flows through a pipe that becomes narrower. Compared to the wider region, the bubbles in the narrow region are
bigger
You have heard the tried and true phrase "it is like running in to a brick wall". Now it is time to dig a little deeper and modify the phrase. Assume you are in a car driving and come in contact with this proverbial brick wall. Your car can do three things after the strike: it can go through, come to stop or bounce back. Select the option which will be the most dangerous to you assuming similar collision times.
bouncing back.
In an experiment water rose by capillary attraction through two columns of soils, one with coarse grains (column 1) and the other with fine gains (column 2). In which column did the water rise to greater height?
column 2
When water flows smoothly in a straight hose, its viscosity causes the water to
convert some of its kinetic energy into thermal energy
When the kinetic energy of a moving object increases by a factor of 4, the magnitude of its momentum
doubles
A drum major is given two batons, one gold and one plastic. He is told that both batons have the same mass. He tries spinning each one and finds that the plastic one is much easier to start and stop spinning. He correctly concludes that the plastic baton, in comparison to the gold baton
has more of its mass distributed towards the center.
A man, with his arms at his sides, is spinning on a light frictionless turntable. When he extends his arms
his angular momentum remains the same.
Consider a block of wood floating on water. If you push down on the top of the block until it is completely submerged, the buoyant force on it
increases
Suppose you are riding on a merry - go - round and you move out to the edge. What happens to the rotational rate of the system?
it decreases because angular momentum is conserved and the moment of inertia increases.
SI unit for viscosity is
kg/(m-s)
Blood flows through a section of a horizontal artery that is partially blocked by a deposit along the artery wall. A hemoglobin molecule moves from the narrow region into the wider region. What happens to the pressure acting on the molecule as it moves from the wider into the narrower region?
pressure decreases
Suppose that there is a partial blockage of the aorta, which normally pumps about 5 L of blood per minute. If the diameter of the aorta were reduced by 30%, what increase in blood pressure gradient would be needed to obtain the normal flow rate? (Assume that Poiseuille's law applies.)
pressure gradient would have to increase by a factor of 4.2
Blood flows through a section of a horizontal artery that is partially blocked by a deposit along the artery wall. A hemoglobin molecule moves from the narrow region into the wider region. What happens to the pressure acting on the molecule as it moves from the narrow to the wider region?
pressure increases
People fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. If there is trouble, a fire fighter can lie under the tent to block the heat from burning trees overhead. The tent helps because
radiation carries heat downward toward the fire fighter and the aluminum tent reflects most of that radiation.
Dimples on a golf ball hit without spin
reduce drag
detergents or wetting agents
reduce the angle of contact.
Some children are riding on the outside edge of a merry-go-round. Ignore friction in the rotation of the merry-go- round. Consider the "system" of the children plus the merry-go-round. At the same time, the children all move towards the center of the merry-go- round. When they do this
the angular momentum of the system stays constant.
When you sit facing a campfire outdoors, your face feels quite warm because
the campfire is radiating heat towards your skin.
A bass has a gas-filled sac or air bladder that allows it to float motionless below the surface of the water. What is the bass's average density?
the density of water
Compare the flight of two golf balls given the same impulse by the club. Which ball will travel a larger distance?
the dimpled ball
Assume a disk and a ring with the same radius roll down an incline of height h and angle theta. If they both start from rest at t = 0, which one will reach the bottom first?
the disk
A sphere, a hoop, and a cylinder, all with the same mass M and the same radius R, are rolling along, all with the same speed v. Which has the most total kinetic energy?
the hoop
A baseball bat with uniform density is cut at the location of its center of mass as shown in the figure. The piece with the smaller mass after the cut is
the piece on the left.
Both the disk and the ring have the same mass, and the same radius. Which has the larger moment of inertia about the center?
the ring
A beaker is filled with water to the rim. Gently you place a toy duck in the beaker and some of the water spills out. The duck floats. The weight of the beaker with the duck floating in it is
the same as its weight before adding the duck
Two objects with different masses collide and stick to each other. Compared to before the collision, the system of two objects after the collision has
the same total momentum but less total kinetic energy.
Two bubbles are connected by a hollow tube plus a valve. What will happen once the valve between the two is opened?
the small bubble will drain into the big bubble.
When blood flows into an aneurysm
the speed decreases and the pressure increases.
In your dorm room you watch the Vols play in an out-of-town game. It is a cliff hangers and the winner will be determined in the last few seconds of play. Everybody is taking their bathroom break right after the game ends. As the toilets flush and hands are washed, the faucet pressure is noticeably reduced, even though the supply pipe to the rooms can carry all the water needed. Why?
the water has to speed up in the supply pipe and therefore the pressure drops in the pipe.
Which of the following assumptions is not made in the derivation of Bernoulli's equation?
there is negligible gravity
Why can't you get all the dust off your car by just squirting water from a hose onto it? Why can't you simply remove dust just by blowing across a surface? Why does dust cling to a fast rotating fan? How can a leaf stay on a car moving at high speed?
this is a consequence of the formation of stationary boundary layer.
A man jumps off of a bridge towards a river below. As he falls, he feels himself spinning forward (clockwise in diagram). To keep from hitting the water head-first, the man should
windmill his arms clockwise to keep upright
Suppose you have a very long straw that can reach from a cup of water on the ground level to the top of a very tall building. When you use a pump to suck on the straw in order to bring water up,
you can bring the water up to only a maximum height in the straw, when the pressure of the water column is approximately equal to the atmospheric pressure.
