phys 1301 midterm
A woman wearing spiked shoes pushes two crates across her frictionless horizontal studio floor If she exerts a horizontal force of 54 N on the smaller crate, then the smaller crate exerts a force on the larger crate that is closest to
45 N
At the same time that rock A is dropped from rest from the top of a building, rock B is thrown horizontally away from the building, also starting at the top. Air resistance is not large enough to worry about. Which of the following statements is correct?
Both rocks reach the ground at the same time.
In which of the following collisions would you expect the kinetic energy to be conserved? A. A bullet passes through a block of wood. B. Two bull elk charge each other and lock horns. C. Two asteroids collide by a glancing blow, but do not actually hit each other, their only interaction being through gravity. D. Two cars with springlike bumpers collide at fairly low speeds.
C, D
Each mass in (Figure 1) is 4.00 kg Find the magnitude of the net gravitational force on mass A due to the other masses in diagram (a) of the figure. Find the direction of the net gravitational force on mass A due to the other masses in diagram (a) of the figure. Find the magnitude of the net gravitational force on mass A due to the other masses in diagram (b) of the figure. Find the direction of the net gravitational force on mass A due to the other masses in diagram (b) of the figure.
F = 1.85e-7 N downward F = 2.04e-7 N to the ball D
The system shown in the figure is released from rest, there is no friction between B and the tabletop, and all of the objects move together. What must be true about the friction force on A?
It acts to the right on A
As planets with a wide variety of properties are discovered outside our solar system, astrobiologists are considering whether and how life could evolve on planets that might be very different from earth. One recently discovered extrasolar planet, or exoplanet, orbits a star whose mass is 0.70 times the mass of our sun. This planet has been found to have 2.3 times the earth's diameter and 29.9 times the earth's mass. For planets in this size range, computer models indicate a relationship between density and composition: Based on these data, what is the most likely composition of this planet?
Mostly iron
Shoes for the sports of bouldering and rock climbing are designed to provide a great deal of friction between the foot and the surface of the ground. On smooth rock these shoes might have a coefficient of static friction of 1.4 and a coefficient of kinetic friction of 0.90. If the person steps onto a smooth rock surface that's inclined at an angle large enough that these shoes begin to slip, what will happen?
She will accelerate down the surface.
A toboggan approaches a snowy hill moving at 13.6 m/s. The coefficients of static and kinetic friction between the snow and the toboggan are 0.47 and 0.33, respectively, and the hill slopes upward at 45.0∘ above the horizontal. Find the magnitude of the acceleration of the toboggan as it is going up the hill. What is the direction of the acceleration as the toboggan is going up the hill? Find the magnitude of the acceleration of the toboggan after it has reached its highest point and is sliding down the hill. What is the direction of the acceleration as the toboggan is sliding down the hill?
a = 9.2 m/s^2 down the hill a=4.6 m/s^2 down the hill
The accelerations due to gravity near the surfaces of the moon, the earth, and Jupiter are 1.6 m/s2, 9.8 m/s2, and 26 m/s2, respectively. Assuming that you like chocolate cake, which would you rather have: Assuming you like chocolate cake, which would you rather have:
a piece of cake that weighs 1 NN on the moon.
An airplane flying at a constant horizontal velocity drops a package of supplies to a scientific mission in the Antarctic. If air resistance is negligibly small, the path of this package, as observed by a person in the plane, is
a straight line downward.
A couple of astronauts agree to rendezvous in space after hours. Their plan is to let gravity bring them together. She has a mass of 65 kg and he has a mass of 72 kg, and they start from rest 21.0 m apart. As a rough approximation, we can model the astronauts as uniform spheres. Find his initial acceleration. Find her initial acceleration If the astronauts' acceleration remained constant, how many days would they have to wait before reaching each other? (Careful! They both have acceleration toward each other.) Would their acceleration, in fact, remain constant? If not, would it increase or decrease?
a1= 9.8e-12 m/s^2 a2= 1.1e-11 m/s^2 t = 16 days No, it would increase.
A ball is thrown horizontally from the top of a building and lands a distance d from the foot of the building after having been in the air for a time T and encountering no significant air resistance. If the building were twice as tall, the ball would have
been in the air a time T(sprt2)
If vector A has components Ax and Ay and makes an angle θ with the +x axis, then
cosθ = Ax/ sqrt (Ax^2 + Ay^2)
A woman starts from her house and begins jogging down her street. In order to keep a record of her workout, she carries a stopwatch and records the time it takes her to reach specific landmarks, such as intersections, school grounds, and churches. Since she knows the distance to each of these landmarks, she is able to tabulate the data shown here: Use the line you drew in Part A to estimate the distance she will jog in 1 hour.
d = 12 km
You are designing a space station and want to get some idea about how large it should be to provide adequate air for the astronauts. Normally, the air is replenished, but for security, you decide that there should be enough to last for two weeks in case of a malfunction. If the space station is to be spherical, what should be its diameter to contain all the air you chose in part A?
d = 5.76 m
A woman starts from her house and begins jogging down her street. In order to keep a record of her workout, she carries a stopwatch and records the time it takes her to reach specific landmarks, such as intersections, school grounds, and churches. Since she knows the distance to each of these landmarks, she is able to tabulate the data shown here: Select the correct plot of the distance jogged versus time with a best-fit line through the data.
first dot on top
A horizontal force accelerates a box across a rough horizontal floor with friction present, producing an acceleration a If the force is now tripled, but all other conditions remain the same, the acceleration will become
greater than 3a
Suppose you are climbing in the High Sierra when you suddenly find yourself at the edge of a fog-shrouded cliff. To find the height of this cliff, you drop a rock from the top and, 11.9 s later, hear the sound of it hitting the ground at the foot of the cliff. Ignoring air resistance, how high is the cliff if the speed of sound is 330 m/s?
h = 520 m
If the vector B has a magnitude of 45 mm and makes an angle of 60 degrees with the +x axis, the vector -B
has a magnitude of 45 mm.
You drop an egg from rest with no air resistance. As it falls,
its mechanical energy is conserved, but its momentum is not conserved.
A horizontal force with a magnitude P pulls two wagons over a horizontal frictionless floor, as shown in the figure (Figure 1). Assume that W1=2800N and W2=700N The tension in the light horizontal rope connecting the wagons is
less than P
Two objects w1=500N and w2=600N are connected by a light wire as shown in the figure, with the wire pulling horizontally on w2. (Figure 1) After this system is released from rest, the tension in the wire will be
less than w1
An airplane whose air speed is 600 mi/h is flying perpendicular to a jet stream whose speed relative to the earth's surface is 100 mi/h. The airplane's speed relative to the earth's surface is
somewhat more than 600 mi/h
A mass m is placed at the rim of a frictionless hemispherical bowl with a radius R and released from rest as in (Figure 1). It then slides down and undergoes a perfectly elastic collision with a second mass 3m sitting at rest at the bottom of the bowl. What is the speed of the first mass just after the collision? Express your answer in terms of acceleration of gravity g and some or all of the variables m and R What is the direction of the first mass just after the collision? What is the speed of the second mass just after the collision? What is the direction of the second mass just after the collision? To what maximum height will the first mass travel after the collision? To what maximum height will the second mass travel after the collision?
sqrt(gR/2) to the left sqrt(gR/2) to the right R/4 R/4
If you throw a stone horizontally out over the surface of a lake, the time it is in the air (i.e., before it hits the water) is determined by only
the height from which you throw it.
A jet fighter pilot wishes to accelerate from rest at 5 g to reach Mach-3 (three times the speed of sound) as quickly as possible. Experimental tests reveal that he will black out if this acceleration lasts for more than 4.8 s . Use 331 m/s for the speed of sound. Will the period of acceleration last long enough to cause him to black out? What is the greatest speed he can reach with an acceleration of 5 g before blacking out?
yes v= 235 m/s
How long would it take you to walk to the moon?
10^8 s
How many steps would you have to take to walk to the moon, assuming that you could somehow walk normally in space?
10^8 steps
A cat runs in a straight line. The figure below shows a graph of the cat's position as a function of time. (Figure 1) Which of the following statements about the cat's motion must be true?
- The cat reverses the direction of its velocity at point b. -At point c, the cat has returned to the place where it started. -The cat's velocity is zero at point b.
A cannonball is fired toward a vertical building 400 m away with an initial velocity of 80 m/s at 36.9∘ above the horizontal. the ball will hit the building in
6.3 s
An object starts from rest and accelerates uniformly. If it moves 2.00 m during the first second, then, during the first 7.00 seconds it will move
98 m
When a mass goes in a horizontal circle with speed V at the end of a string of length L on a frictionless table, the tension in the string is T. If the speed of this mass were tripled, but all else remained the same, the tension would be
9T
A ball thrown horizontally from the top of a building hits the ground in 1.00 s If it had been thrown with twice the speed in the same direction, it would have hit the ground in
1.00 s
Which of the following statements about average speed is correct?
- If the average speed is zero, then the average velocity must be zero. - The average speed can never be less than the magnitude of the average velocity.
A student measures the force required to stretch a spring by various amounts and makes the graph shown in (Figure 1), which plots this force as a function of the distance the spring has stretched. Does this spring obey Hooke's law? How do you know? What is the force constant of the spring? What force would be needed to stretch the spring a distance of 19 cm from its unstretched length, assuming that it continues to obey Hooke's law?
- Yes, the spring obeys Hooke's law because the graph of F versus x is linear. - k = 150 N/m - F = 29 N
A Ferris wheel with a radius of 14.0 m is turning about a horizontal axis through its center, as shown in the figure below. (Figure 1)The linear speed of a passenger on the rim is constant and equal to 7.50 m/s What is the magnitude of the passenger's acceleration as she passes through the lowest point in her circular motion? What is the direction of the passenger's acceleration as she passes through the lowest point in her circular motion? What is the magnitude of the passenger's acceleration as she passes through the highest point in her circular motion? What is the direction of the passenger's acceleration as she passes through the highest point in her circular motion? How much time does it take the Ferris wheel to make one revolution?
- a = 4.02 m/s ^2 - upward - a = 4.02 m/s ^2 - Downward - t = 11.7 s
For a fifth set of maneuvers, the astronaut's partner calculates her average acceleration over the 2 s interval to be -0.5 m/s2. If the initial velocity of the astronaut was -0.3 m/s, what was her final velocity? Did she speed up or slow down over the 2 s interval?
-1.3 m/s She sped up
In human lungs, oxygen and carbon dioxide are exchanged in the blood within many small sacs called alveoli. Alveoli provide a large surface area for gas exchange. Recent careful measurements show that the total number of alveoli in a typical human lung pair is about 480×10^6and that the average volume of a single alveolus is 4.2×10^6μm^3. It may be useful to recall the equation for the volume of a sphere, V=4/3πr^3, and the equation for the area of a sphere, A=4πr^2 Assuming the alveoli are spherical, what is the diameter of a typical alveolus?
0.20 mm
Some plants disperse their seeds by having the fruit split and contract, propelling the seeds through the air. The trajectory of these seeds can be determined by using a high-speed camera. In one type of plant, seeds are projected at 20 cm above ground level with initial speeds between 2.3 m/s and 4.9 m/s . The launch angle is measured from the horizontal, with +90∘ corresponding to an initial velocity straight upward and −90∘ straight downward. About how long does it take a seed launched at 90∘ at the highest possible initial speed to reach its maximum height? Ignore air resistance.
0.50 s
As planets with a wide variety of properties are discovered outside our solar system, astrobiologists are considering whether and how life could evolve on planets that might be very different from earth. One recently discovered extrasolar planet, or exoplanet, orbits a star whose mass is 0.70 times the mass of our sun. This planet has been found to have 2.3 times the earth's diameter and 7.9 times the earth's mass. For planets in this size range, computer models indicate a relationship between density and composition: Observations of this planet over time show that it is in a nearly circular orbit around its star and completes one orbit in only 255.7 days. How many times the orbital radius r of the earth around our sun is this exoplanet's orbital radius around its sun? Assume that the earth is also in a nearly circular orbit.
0.70 r
A DNA molecule, with its double-helix structure, can in some situations behave like a spring. Measuring the force required to stretch single DNA molecules under various conditions can provide information about the biophysical properties of DNA. A technique for measuring the stretching force makes use of a very small cantilever, which consists of a beam that is supported at one end and free to move at the other end, like a tiny diving board. The cantilever is constructed so that it obeys Hooke's law—that is, the displacement of its free end is proportional to the force applied to it... Based on the figure (Figure 2), how much elastic potential energy is stored in the DNA when it is stretched 45 nm?
1.0e-19 J
Archerfish are tropical fish that hunt by shooting drops of water from their mouths at insects above the water's surface to knock them into the water, where the fish can eat them. A 65 g fish at rest just on the water's surface can expel a 0.30 g drop of water in a short burst of 5.0 ms. High-speed measurements show that the water has a speed of 5.0m/s just after the archerfish expels it. What is the momentum of one drop of water immediately after it leaves the fish's mouth? What is the speed of the archerfish immediately after it expels the drop of water?
1.5e-3 kg m/s 0.028 m/s
Shoes for the sports of bouldering and rock climbing are designed to provide a great deal of friction between the foot and the surface of the ground. On smooth rock these shoes might have a coefficient of static friction of 1.5 and a coefficient of kinetic friction of 0.90. A person wearing these shoes stands on a smooth horizontal rock. She pushes against the ground to begin running. What is the maximum horizontal acceleration she can have without slipping?
1.5g
Two carts, one twice as heavy as the other, are at rest on a horizontal frictionless track. A person pushes each cart with the same force for 8.00 s If the kinetic energy of the lighter cart after the push is K, the kinetic energy of the heavier cart is
1/2 K
On flat ground, a 70-kg person requires about 300 W of metabolic power to walk at a steady pace of 5.0 km/h (1.4 m/s). Using the same metabolic power output, that person can bicycle over the same ground at 10 km/h. Based on these data, how does the energy used in biking 1 km compare with that used in walking 1 km? Biking takes
1/2 of the energy of walking the same distance.
You are designing a space station and want to get some idea about how large it should be to provide adequate air for the astronauts. Normally, the air is replenished, but for security, you decide that there should be enough to last for two weeks in case of a malfunction. Estimate how many cubic meters of air an average person breathes in two weeks. A typical human breathes about 1/2 L per breath and takes 12 breaths per minute.
100 m^3
A physics student measures the energy stored in a spring as a function of the distance it is stretched beyond its undistorted length. Her data are given in the table. Draw a linearized graph of the data by plotting the spring's energy as a function of the square of the distance it is stretched. (PIC) Using a linear "best fit" to the data, determine the force constant of the spring.
1000 N/m
A 9.00 kg point mass and a 13.0 kg point mass are held in place 50.0 cm apart in deep space. They are both released at the same time. Find the magnitude of the acceleration of the 13.0 kg point mass the moment after they are released. Find the direction of the acceleration of the 13.0 kg point mass the moment after they are released. Find the magnitude of the acceleration of the 9.00 kg point mass the moment after they are released. Find the direction of the acceleration of the 9.00 kgkg point mass the moment after they are released. As the particles begin to move, is their acceleration constant? Explain.
2.40e-9 m/s^2 acceleration of the 13.0 kg point mass is towards the 9.00 kg mass a= 3.47e-9 m/s^2 acceleration of the 13.0 kg point mass is towards the 9.00 kg mass The acceleration is not constant as the particles move because the distance r between the particles decreases, which causes the acceleration to increase.
An object traveling at speed V in a circle of radius R/2 has an acceleration a If both speed and radius are doubled, the new acceleration will be
2a
A cannonball is fired horizontally from a 240-m-high cliff toward a vertical building 720 m away with an initial velocity of 120 m/s. The cannonball will hit the building in
6.0 s
A stone is thrown horizontally with a speed of 22.0 m/s from the top of a vertical cliff at the edge of a lake. If the stone hits the water 4.00 s later, the height of the cliff is closest to
80.0 m
For an initial speed v0, what is the maximum height reached by a projectile when θ 0 = 30 ∘
8g
Two lumps of clay having equal masses and speeds, but traveling in opposite directions, collide and stick together. Which of the following statements about this system of lumps must be true? A. The momentum of the system is conserved during the collision. B. The kinetic energy of the system is conserved during the collision. C. The two masses lose all their kinetic energy during the collision. D. The velocity of the center of mass of the system is the same after the collision as it was before the collision.
A, C, D
Two masses, M and 8 M, are at rest on a horizontal frictionless table with a compressed spring of negligible mass between them When the spring is released, A. The two masses receive equal magnitudes of momentum. B. The two masses receive equal amounts of kinetic energy from the spring. C. The heavier mass gains more kinetic energy than the lighter mass. D. The lighter mass gains more kinetic energy than the heavier mass.
A, D
Which of the following statements is true for an elastic collision? A. Both momentum and kinetic energy are conserved. B. Momentum is conserved, but kinetic energy is not conserved. C. Kinetic energy is conserved, but momentum is not conserved. D. The amount of momentum lost by one object is the same as the amount gained by the other object. E. The amount of kinetic energy lost by one object is the same as the amount gained by the other object.
A, D, E
As planets with a wide variety of properties are discovered outside our solar system, astrobiologists are considering whether and how life could evolve on planets that might be very different from earth. One recently discovered extrasolar planet, or exoplanet, orbits a star whose mass is 0.70 times the mass of our sun. This planet has been found to have 2.3 times the earth's diameter and 41.8 times the earth's mass. For planets in this size range, computer models indicate a relationship between density and composition: How many times the acceleration due to gravity g near the earth's surface is the acceleration due to gravity near the surface of this exoplanet?
About 7.9g
In human lungs, oxygen and carbon dioxide are exchanged in the blood within many small sacs called alveoli. Alveoli provide a large surface area for gas exchange. Recent careful measurements show that the total number of alveoli in a typical human lung pair is about 480×10^6and that the average volume of a single alveolus is 4.2×10^6μm^3. It may be useful to recall the equation for the volume of a sphere, V=4/3πr^3, and the equation for the area of a sphere, A=4πr^2 Individuals vary considerably in total lung volume. The accompanying graph (Figure 1) shows the results of measuring the total lung volume and average alveolar volume of six individuals. From these data, what can you infer about the relationship among alveolar size, total lung volume, and number of alveoli per individual?
As the total volume of the lungs increases, the volume of the individual alveoli remains constant and the number of alveoli increases.
Which of the following statements is true for an inelastic collision? A. Both momentum and kinetic energy are conserved. B. Momentum is conserved, but kinetic energy is not conserved. C. Kinetic energy is conserved, but momentum is not conserved. D. The amount of momentum lost by one object is the same as the amount gained by the other object. E. The amount of kinetic energy lost by one object is the same as the amount gained by the other object.
B, D
A 72.0 kg person is put on an exercise program by a physical therapist, the goal being to burn up 540 food calories in each daily session. Recall that human muscles are about 21.0 % efficient in converting the energy they use up into mechanical energy. The exercise program consists of a set of consecutive high jumps, each one 45.0 cm into the air (which is pretty good for a human) and lasting 1.50 s, on the average. How many jumps should the person do per session? How much time should be set aside for each session? Do you think that this is a physically reasonable exercise session?
N = 1500 t= 37 min no
A crate slides up an inclined ramp and then slides down the ramp after momentarily stopping near the top. This crate is acted upon by friction on the ramp and accelerates both ways. Which statement about this crate's acceleration is correct?
The acceleration going up the ramp is greater than the acceleration going down.
You drag a heavy box along a rough horizontal floor by a horizontal rope Identify the reaction force to the pull of the rope on the box. Identify the reaction force to the friction force on the box. Identify the reaction force to the normal force on the box. Identify the reaction force to the weight of the box.
The box pulls on the rope. The friction force is a horizontal force applied to the box by the floor. The reaction force is a horizontal force in the opposite direction applied by the box to the floor. The normal force is an upward force applied by the floor to the box. The reaction force is a downward force applied by the box to the floor. The weight of the box is a downward force applied to the box by the earth. The reaction force is an upward force applied to the earth by the box.
A woman normally weighs 125 lb She is standing on a spring scale in an elevator that is traveling downward, but slowing up.
The scale will read more than 125 lb
Cart A, of mass 2 kg , is initially moving to the left and collides with cart B, which has a mass of 7 kg and is initially at rest. (See the figure below. (Figure 1) After the collision, cart A will
move back to the right.
Suppose you are climbing in the High Sierra when you suddenly find yourself at the edge of a fog-shrouded cliff. To find the height of this cliff, you drop a rock from the top and, 11.9 s later, hear the sound of it hitting the ground at the foot of the cliff. Suppose you had ignored the time it takes the sound to reach you. In that case, would you have overestimated or underestimated the height of the cliff?
overestimated the height of the cliff
Your boat departs from the bank of a river that has a swift current parallel to its banks. If you want to cross this river in the shortest amount of time, you should direct your boat
perpendicular to the current.
Dancers experience large forces associated with the jumps they make. For example, when a dancer lands after a vertical jump, the force exerted on the head by the neck must exceed the head's weight by enough to cause the head to slow down and come to rest. The head is about 9.4% of a typical person's mass. Video analysis of a 69 kg dancer landing after a vertical jump shows that her head slows down from 4.2 m/s to rest in a time of 0.20 s Compared with the force her neck exerts on her head during the landing, the force her head exerts on her neck is:
the same
A block of ice with a mass of 2.50 kg is moving on a frictionless, horizontal surface. At t=0, the block is moving to the right with a velocity of magnitude 6.00 m/s. Calculate the magnitude of the velocity of the block if a force of 5.50 N directed to the right has been applied to it for 5.00 s Find the direction of the velocity of the block if a force of 5.50 N directed to the right has been applied to it for 5.00 s Calculate the magnitude of the velocity of the block if instead a force of 7.00 N directed to the left has been applied to it for 5.00 s Find the direction of the velocity of the block if a force of 7.00 N directed to the left has been applied to it for 5.00 s
v = 17.0 m/s to the right v = 8.00 m/s to the left
A woman starts from her house and begins jogging down her street. In order to keep a record of her workout, she carries a stopwatch and records the time it takes her to reach specific landmarks, such as intersections, school grounds, and churches. Since she knows the distance to each of these landmarks, she is able to tabulate the data shown here: Use the line you drew in Part A to estimate the speed at which she was jogging.
v = 3.3 m/s
