Physics exam 3
A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?
(rg)^1/2
A thin hoop with a radius of 10 cm and a mass of 3.0 kg is rotating about its center with an angular speed of 3.5 rad/s. What is its kinetic energy?
0.18 J
The flywheel of a machine is rotating at 126 rad/s. Through what angle will the wheel be displaced from its original position after 6.0 s?
0.32 revolutions
A mass of 1000 kg hangs at the end of a steel rod 5.0 m in length. The diameter of the rod is 0.80 cm and Young's modulus for the rod is 210,000 MN/m2. What is the elongation of the rod?
0.46 cm
A cable is 100-m long and has a cross-sectional area of 1 mm2. A 1000-N force is applied to stretch the cable. The elastic modulus for the cable is 1.0 × 1011 N/m2. How far does it stretch?
1.0 m
A race car, traveling at a constant speed of 50 m/s, drives around a circular track of radius 250 m. What angular acceleration does it experience?
1.0 × 10^1 rad/
Two horizontal curves on a bobsled run are banked at the same angle, but one has twice the radius of the other. The safe speed (no friction needed to stay on the run) for the smaller radius curve is V. Therefore, the safe speed on the larger radius curve is
1.4 V
A 0.600-mm diameter wire stretches 0.5% of its length when it is stretched with a tension of 20 N. What is the Young's modulus of this wire?
1.41 × 10^10 N/m2
What is the centripetal acceleration of a point on the perimeter of a bicycle wheel of diameter 70. cm when the bike is moving 8.0 m/s?
1.8E2 m/s^2
A ship that weighs 10,000 tons (mass 10 million kg) must displace what volume of fresh water in order to float
10^4 m^3
A spherically symmetric planet has four times the Earth's mass and twice its radius. If a jar of peanut butter weighs 12. N on the surface of the Earth, how much would it weigh on the surface of this planet?
12 N
A 3.00-m long tube with circular crosssection tapers from a diameter of 10.0 cm at one end down to 4.00 cm at the other end. If an incompressible fluid flows irrotationally through the tube at a speed of 2.00 m/s at the 10.0 cm end, what is the speed of the flow at the 4.00 cm diameter end?
12.5 m/s
James moves in a circular path (radius 15.0 m) with a speed of 60.0 m/s. His ANGULAR VELOCITY is
120/π rpm.
Instead of cables, a hydraulic lift raises an elevator weighing 2.5 kiloNewtons. The input piston has a 2.0 cm diameter and the lift piston has a 28. cm diameter (See Fig. 9-3). What minimum force must be applied to the input piston?
13. N
Air is flowing through a rocket nozzle. Inside the rocket the air has a density of 5.25 kg/m3 and a speed of 1.20 m/s. The interior diameter of the rocket is 15.0 cm. At the nozzle exit, the diameter is 2.50 cm and the density is 1.29 kg/m3. What is the speed of the air when it leaves the nozzle?
176 m/s
A space station of diameter 40. meters is turning about its axis at a constant rate. What is the period of revolution of the space station if the outer rim experiences an acceleration of 2.5 m/ ?
18 s
The moment of inertia of a solid cylinder about its axis is given by 0.5M . If this cylinder rolls without slipping, the ratio of its rotational kinetic energy to its translational kinetic energy is
1:2
Consider two uniform solid spheres where both have the same diameter, but one has twice the mass of the other. The ratio of the larger moment of inertia to that of the smaller moment of inertia is
2
A pulsar (a rotating neutron star) emits pulses at a frequency of 0.40 kHz. The period of its rotation is
2.5 ms
A rock is suspended from a scale reads 20.0 N. A beaker of water is raised up so the rock is totally submerged in the water. The scale now reads 12.5 N. What is the density of the rock?
2.67 × 10^3 kg/m^3
A uniform rod has a weight of 40. N and a length of 1.0 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end), as shown in Fig. 8-7. What is the magnitude of the torque exerted by the string about a horizontal axis which passes through the hinge and is perpendicular to the rod?
20 mN
A flywheel, of radius 1 m, is spinning with a constant angular velocity of 2 rad/s. What is the centripetal acceleration of a point on the wheel's rim?
4 m/s2
23) A car traveling 20 m/s rounds an 80 m radius horizontal curve with the tires on the verge of slipping. How fast can this car round a second curve of radius 320 m? (Assume the same coefficient of friction between the car's tires and each road surface.)
40 m/s
An incompressible fluid flows steadily through a pipe that has a change in diameter. The fluid speed at a location where the pipe diameter is is What is the fluid speed at a location where the diameter has narrowed to
5.12 m/s
A 13000 N vehicle is to be lifted by a 25 cm diameter hydraulic piston. What force needs to be applied to a 5.0 cm diameter piston to accomplish this?
520 N
An ice skater has a moment of inertia of 5.0 kg∙m2 when her arms are outstretched. At this time she is spinning at 3.0 revolutions per second (rps). If she pulls in her arms and decreases her moment of inertia to 2.0 kg∙m2, how fast will she be spinning?
7.5 rps
A seesaw made of a plank of mass 10.0 kg and length 3.00 m is balanced on a fulcrum 1.00 m from one end of the plank. A 20.0-kg mass rests on the end of the plank nearest the fulcrum. What mass must be on the other end if the plank remains balanced?
7.50-kg
A spherical inflated balloon is submerged in a pool of water. If it is further inflated so that its radius doubles, how is the buoyant force affected?
8x larger
A copper wire is found to break when subjected to minimum tension of 36. N. If the wire diameter were half as great, we would expect the wire to break when subjected to a minimum tension of
9.0 N
Consider a rigid body that is rotating. Which of the following is an accurate statement?
All points on the body are moving with the same angular velocity.
The pressure differential across a wing cross section due to the difference in air flow is explained by
Bernoulli's equation.
Which one of the following would be expected to have the smallest BULK MODULUS?
Helium vapor
A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-round's center. If the boy and girl are of equal mass, which statement is true about the boy's moment of inertia with respect to the axis of rotation?
His moment of inertia is 4 times the girl's.
A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw?
Nothing, the seesaw will still be balanced.
A solid cylinder and a hollow cylinder have the same mass and the same radius. Which statement is true concerning their moment of inertia about an axis through the exact center of the flat surfaces?
The hollow cylinder has the greater moment of inertia.
A heavy seesaw is out of balance. A lightweight girl sits on the end that is tilted downward, and a heavy boy sits on the other side so that the seesaw now balances. If the boy and girl both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw?
The side the girl is sitting on will once again tilt downward.
When a rigid body rotates about a fixed axis all the points in the body have the same angular speed. (T/F)
True
The condition for rolling without slipping is that the center of mass speed is
Vcm = r ω
Consider a solid object which is subjected to a net torque. That object will experience which of the following?
an angular acceleration
Stress is
applied force per cross-sectional area
A ball, solid cylinder, and a hollow pipe all have equal masses and radii. If the three are released simultaneously at the top of an inclined plane, which will reach the bottom first?
ball
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger centripetal acceleration?
child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger linear displacement?
child A
As a helium-filled dirigible rises in the atmosphere, the buoyancy force is expected to
decrease
When you are scuba diving, the pressure on your face plate
depends only on your depth, and not on how you are oriented.
An object completely submerged in water must either rise or fall. (T/F)
false
An object in motion with constant speed along a straight line can never have nonzero angular momentum.
false
If an object is in unstable equilibrium, any small displacement results in a restoring force or torque, which tends to return the object to its original equilibrium position.
false
When a rigid body rotates about a fixed axis all the points in the body have the same centripetal acceleration. (T/F)
false
When a rigid body rotates about a fixed axis all the points in the body have the same linear displacement
false
When a rigid body rotates about a fixed axis all the points in the body have the same linear displacement. (T/F)
false
When a rigid body rotates about a fixed axis all the points in the body have the same tangential speed. (T/F)
false
The speed of Halley's comet, while traveling in its elliptical orbit around the sun,
increases as it nears the sun.
A pencil balanced on its tip such that it does not move
is in unstable equilibrium
An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his moment of inertia about the axis of rotation?
it decreases
An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his angular momentum about the axis of rotation?
it does not change
An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his rotational kinetic energy about the axis of rotation?
it increases
Does the centripetal force acting on an object do work on the object?
no, because the force and the displacement of the object are perpendicular
The weight that will cause a wire of diameter d to stretch a given distance, for a fixed length of wire, is
proportional to d^2.
If a constant net torque is applied to an object, that object will
rotate with constant angular acceleration.
Two equal forces are applied to a door at the doorknob. The first force is applied perpendicular to the door; the second force is applied at 30° to the plane of the door. Which force exerts the greater torque?
the first applied perpendicular to the door
Strain is
the ratio of the change in length to the original length.
Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the greater torque?
the second at the doorknob
A submarine rests on the sea bottom. The normal force exerted upon the sub by the sea-floor is equal to
the weight of the sub less the weight of the displaced water.
Marilyn (M) and her sister Sheila (S) are riding on a merry-go-round, as shown in Fig. 7-3 (bird's-eye view). Which of the following is true?
they have different speeds, but the same angular velocity
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular speed?
they have the same non zero angular speed
Kepler's discovery that T^2/r^3 = K applies
to elliptical orbits where r is the average distance.
If an external pressure is applied to a confined fluid, the pressure at every point within the fluid increases by that amount. (T/F)
true
Unbalanced torques produce rotational accelerations, and balanced torques produce rotational equilibrium.
true
When a rigid body rotates about a fixed axis all the points in the body have the same angular displacement (T/F)
true
When a rigid body rotates about a fixed axis all the points in the body have the same angular speed.
true
The slope of the straight line shown on the graph in Fig. 9-1 is called the
young's modulus
