2018+Rotational+Motion

Rotational Motion


 * Wednesday**





Thursday



Monday





these answers use sig figs (boo!)



Tuesday











__An__ __Answer key:__ 1) 2.125 E-2 rev/s 2) 9.76 s 3) 0.99 m/s, 1.47 N 4) 40.43 degrees north or south 5) 85 grams, 76.1 degrees above horizontal (that's the direction it FLIES OFF AT). It breaks at 76.1 degrees past the initial position in quadrant 4.

Wednesday



for slide 4: the answer using the law of cosines as 75.51 degrees. The answer on the powerpoint is the approximation regular physics used two years ago.

__PRACTICE TEST__

1) When do you need to change your calculator mode from degrees to radians or vice versa? (I know this is a different kind of question but it keeps coming up in class so I thought everyone should be aware of the answer) 2) What is the Earth's angular velocity? (Earth's radius = 6371 km) 3) What is the tangential velocity of people living on the equator? Living in Lima, Peru? Living in Woodbury, MN? 4) Would the acceleration of falling objects on Earth increase or decrease if the world stopped spinning? 5) A kid is sitting at the edge of a merry-go-round that his friend spins faster and faster. At the moment the kid flies off the edge which two forces are equal? What are the equations for those two forces? 6) Why is centrifugal force not considered an actual force? 7) Convert the distance formula into a circular system. 8) Use dimensional analysis to show that the equation for centripetal force gives you units of Newtons. 9) Explain the difference between tangential and angular velocity. Do the same for tangential and angular acceleration.

11) A penny is placed on a record that is increasingly spinning faster and faster. At a certain angular velocity the penny flies off. What is the equation for the unknown radius of the record? 12) A mysterious planet with radius 4.7 E 9 meters has a gravitational pull of 15 m/s2 but it's spinning so #|fast that a 50 kg rock at the equater no longer fall downward. At what latitudes (north and south) will the same rock have a downward acceleration of 10 m/s2? 13) A 200 gram ball on a 0.75 meter string has #|initial angular velocity of 1.5 rad/s. The person spinning it supplies a force that provides an angular acceleration of 2.0 rad/s2. The string will break when the tension reaches 150 N. How many seconds until the string breaks? What angle will the ball go flying off at? Assume the ball starts at 0 #|degrees and spins counter-clockwise.

ANSWER KEY

1) You need to be careful about your mode when using trig function (tan, sin, cos) 2) 7.27 * 10-5 rad/s 3) Woodbury: 327.51 m/s. Lima: 453.05 m/s. THANKS ELLIE, GRACIE AND LAUREN!) 4) It would increase because there would be no force opposing gravity (but the increase would be really tiny!) 5) The centrifugal force and the force of static friction would be equal. ma (centripetal) = "mew (static)"mg 6) It's really just the effects of inertia. 7) "theta equals omega-initial times time plus one half alpha times time squared" 8) hard to show on here, but set force = mrw^2 and solve it 9) Answers will vary