Physics lab 6

Given w = 62.8 rad/s and R = 0.5 m for an object moving in uniform circular motion. In hertz what is the frequency of the motion? (Use pi = 3.14) a. 1.0 Hz b. 10.0 Hz c. 20 Hz d. 6.2 Hz e. 6.28 Hz

b. 10.0 Hz Response Feedback: w = 2*Pi*f, therefore f = w / (2*Pi) f = 62.8 / (2*Pi) = 10.0 Hz

One complete revolution corresponds to 360 degrees which corresponds to ____________. A radian is equal to approximately ___________. a. Pi radians; 57.29 degrees b. 2*Pi radians; 57.29 degrees c. Pi/4 radians; 60 degrees d. Pi/2 radians; 60 degrees e. 2 radians; 30 degrees

b. 2*Pi radians; 57.29 degrees

Given w = 62.8 rad/s and R = 0.50 m for an object moving in uniform circular motion with period T. In m/s what is the linear speed of the motion? a. 62 m/s b. 31 m/s c. 31.4 m/s d. 12.3 m/s e. 6.28 m/s

b. 31 m/s Answer Feedback: Since v = Rw, v = 0.50 * 62.8 = 31 m/s

"An object's velocity remains constant unless acted upon by a net external force" is a statement of Newton's ________________. a. Zeroth Law b. First Law c. Second Law d. Third Law e. Law of Universal Gravitation

b. First Law

What was a source of error in your experiment? a. Tension in string b. Reading the values of w from the graph. c. Measurement of mass d. All of the above e. B and C

b. Reading the values of w from the graph.

Why is it necessary to push the trolley out to the end of the track before you start increasing the angular velocity? a. friction will keep trolley from moving out and it will never reach the end of the track b. if angular velocity is increased to fast, trolley will fly off the track and break or hit someone. c. You measured the radius to be at the end of the track so that is where the trolley needs to be d. All of the above e. A and B

b. if angular velocity is increased to fast, trolley will fly off the track and break or hit someone.

As the trolley mass and radius are held constant and the hanging mass is increased, the angular velocity . . . a. decreases b. increases c. remains the same d. goes to zero e. stabilizes

b. increases

In m/s what is the linear speed of a point at the equator on the surface of the earth? Assume the radius of the earth to be 6.40x10^3 kilometers. HINT: the earth rotates 2*Pi radians in 24.0 hours OR one rotation per day OR 360 degrees in 24.0 hours. a. 707 m/s b. 0.465 m/s c. 465 m/s d. 585 m/s e. 465.4 m/s

c. 465 m/s Answer Feedback: Be careful to correctly convert 24 hours into seconds. Since v = Rw, and w = 2Pi/( number of seconds in a day ), then v = R*[2Pi/(24*60*60)] v = 465 m/s

A car of mass 2000.0 kg is traveling at a constant speed of 85 m/s in a curve with radius 15 m. What is the centripetal acceleration? a. 1.7x10^5 m/s^2 b. 482 m/s^2 c. 480 m/s^2 d. 5.7 m/s^2 e. 5.70 m/s^2

c. 480 m/s^2 Answer Feedback: Since v = Rw then w = v / R. Centripetal acceleration = Rw^2 = R(v^2/R^2) = v^2/R = 85^2/15 = 480 m/s^2

Given w = 62.8 rad/s and R = 0.50 m for a 0.50 kg object moving in uniform circular motion, what is the centripetal force causing the object to accelerate? a. 15.7 N b. 985 N c. 990 N d. 500 N e. 246 N

c. 990 N Answer Feedback: Since F = ma = m(Rw^2) Then F = 0.50(0.50*62.8^2) = 990 N

Uniform circular motion means the a. velocity of the revolving mass is constant b. magnitude of the velocity vector increases at a constant rate c. direction of the acceleration is constant d. rate of change of the velocity vector opposes the acceleration e. speed of the revolving mass is constant

e. speed of the revolving mass is constant Answer Feedback: Velocity is a speed and a direction. If the mass is revolving, its direction (and thus its velocity) cannot be constant. Uniform circular motion means the speed of the revolving mass is constant.

If a centripetal acceleration is experienced or measured it necessarily follows that a. a balanced force acts in the direction of the acceleration b. the instantaneous velocity vector is in the same direction as the measured acceleration c. a reactive centrifugal acceleration exists d. a centrifugal force acts in the direction of the acceleration e. the direction of the acceleration is in the direction of the change in velocity vector

e. the direction of the acceleration is in the direction of the change in velocity vector

Since the radius of the trolley where the angular velocity is measured is smaller than the measured radius used in the calculation we expect the calculated centripetal force to be __________ actual. a. larger than b. smaller than c. the same as d. opposite of e. None of the above

a. larger than

Why do you find the percent difference between the two centripetal force values and not the percent error? a. Both values were calculated, therefore neither one was an accepted value b. Because there was no error in the experiment c. There was such a big difference between the two values d. Both A and B e. Both B and C

a. Both values were calculated, therefore neither one was an accepted value

Given w = 62.8 rad/s and R = 0.5 m for an object moving in uniform circular motion, what is the period of the motion in seconds?(Use pi = 3.14) a. 0.100 s b. 0.1 s c. 10 s d. 100 s e. 6.28 s

a. 0.100 s

If the trolley mass increases and the hanging mass and radius are held constant, the angular velocity . . . a. decreases b. increases c. remains the same d. goes to zero e. stabilizes

a. decreases

In rad/s what is the angular speed of the earth? Assume the radius of the earth to be 6.40x10^3 km and the period of the Earth's rotation to be 23.9 hours. a. 7.27x10^-5 rad/s b. 2.62x10^-1 rad/s c. 7.272x10^-5 rad/s d. 5.43x10^5 rad/s e. 465 rad/s

a. 7.27x10^-5 rad/s

In the graph of Mg/m vs. w^2, what does the y-intercept represent? a. friction b. angular velocity c. radius of pulley d. stretching of string e. mass

a. friction

At what angular speed would the earth have to rotate in order for objects at the equator to have no weight. Assume the radius of the earth to be 6.40E03 kilometers. HINT: weight = mg; g = 9.81 m/s^2. a. 0.00124 rad/s b. 0.071 rad/s c. 6125 rad/s d. 0.0012 rad/s e. 1.53x10^-6 rad/s

a. 0.00124 rad/s

In this experiment, your motor was held in contact with the wheel by a rubber band. Why was that necessary? Why couldn't you simply hold the motor in contact? a. In order to maximize control of angular velocity measurements, the motor must be held firm against the wheel at a constant pressure b. You simply did not have enough hands to hold the hanger, adjust the speed, and hold the motor in contact with the wheel. c. A and B d. Rubber bands rather than a more firm connection were used to allow for fluctuations in wheels spin e. In order to provide variable pressure

c. A and B Answer Feedback: also, you did not have enough hands to hold the hanger, adjust the speed, and hold the motor in contact with the wheel.

Centripetal force is directed radially inward for an object traveling in a circle. What is applying the centripetal force? a. Mass of the trolley times the angular velocity squared divided by radius b. Friction of trolley against the sides c. The tension in the string d. You are applying the force by holding the string e. The rotating object itself

c. The tension in the string

A centripetal force of 318 N acts on mass m = 2 kg moving in uniform circular motion of radius R = 1 m with w = 12.6 rad/s. No useful work is done by the centripetal force because a. centripetal force is fictitious b. the centripetal force is balanced by centrifugal force c. centripetal force acts perpendicular to the instantaneous displacement of the revolving mass d. all of the work is dissipated to friction e. the tangential component of the centripetal force equals the radial component

c. centripetal force acts perpendicular to the instantaneous displacement of the revolving mass Answer Feedback: Remember: centripetal force is real; centrifugal force is fictitious. No useful work is done because centripetal force acts perpendicular to the instantaneous displacement of the revolving mass.

A 0.500 kg mass is attached to the end of a 1.50 m cord . The ball is whirled in a horizontal circle with a radius equal to the length of the string. If the cord can withstand a maximum tension of 50.0 N, what is the maximum speed the ball can have before the cord breaks? a. 0.75 m/s b. 150. m/s c. 15 m/s d. 12.2 m/s e. 12.25 m/s

d. 12.2 m/s Answer Feedback: Since F =mv^2/R Then v = square root of ( FR/m ) = square root of ( 50.0*1.50 / 0.500 ) = 12.2 m/s

Centripetal literally means ____________ while centrifugal is defined as ______________. a. inside of center; outside of center b. radially outward; radially inward c. center-fleeing; center-seeking d. center-seeking; center-fleeing e. eccentric (off-center); intrinsic

d. center-seeking; center-fleeing

The tendency of an object to oppose a change in its state of relative rest or constant velocity and measured by its mass is called a. momentum b. acceleration c. centripetal force d. inertia e. centrifugal force

d. inertia

The natural unit of angular displacement defined as the angle subtended by an arc length equal to one radius is called the a. degree (which is 1/360 of a complete revolution) b. mil (which is 1/6400 of a complete revolution) c. minute of arc (1/60 of 1/360 of a complete revolution) d. radian e. second of arc (1/60 of 1/60 of 1/360 of a complete revolution)

d. radian

Given w = angular speed in rad/sec and R = radius of the circular path of an object moving in uniform circular motion with period T and frequency f. The linear speed v of the object is expressed as a. v = w/R b. v = 2*Pi*f c. v = R*w^2 d. v = R*w e. v = R/w

d. v = R*w

Given w = angular speed in rad/sec and R = radius of the circular path of an object moving in uniform circular motion with period T and frequency f. Which of the following is NOT an expression of centripetal force? a. F = mRw^2 b. F = (mv^2)/R c. F = (4PI^2)*(f^2)*R*m d. F = ((4Pi^2)*R*m)/T^2 e. F = m*2*Pi*w

e. F = m*2*Pi*w Answer Feedback: since Rw^2 is centripetal acceleration, F = mRw^2 is just another way of stating F = ma.

If a centripetal acceleration is experienced or measured it necessarily follows that a. a balanced force acts in the direction of the acceleration b. the instantaneous velocity vector is in the same direction as the measured acceleration c. a reactive centrifugal acceleration exists d. a centrifugal force acts in the direction of the acceleration e. an unbalanced force acts in the direction of the acceleration

e. an unbalanced force acts in the direction of the acceleration

What is the term used to describe a fictitious force that seems to be directed outward along the radius of a circle acting on the rotating object of interest in uniform circular motion if the observer is located in the system of reference that moves with the object? a. force of friction b. force of gravity c. reaction to centripetal force d. centripetal force e. centrifugal force

e. centrifugal force