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Solved University-Physics Problems

Physics 1.-  Mechanics:   Accelerated Circular Motion 

Javier Montenegro Joo

jmj@VirtualDynamicsSoft.com

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  Accelerated Circular Motion.-  
     
  [1]  A disk of 2.5 kg and 1 m diameter is rotating at 3000 rpm when it is disconnected from the source of energy that keeps it rotating. For the moment just before disconnection calculate: (a) angular speed of the disc (b) tangential speed of a point on the edge of the disc, (c) centripetal acceleration of a point on the edge of the disc (d) If the disk stops 30 s after disconnection, determine how many turns are completed during that time.

Solution.-

 
                   

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This module displays an application of the conservation of energy and linear momentum during collisions.

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  [2]  A 2.50 m diameter disk starts rotating with an angular speed of 1.75 rad/s and a constant acceleration of 1.60 rad/s2 .  For a dot at the edge of the disk and for 1.50s after initiated the motion, calculate: (a) Displacement, (b) Angular velocity, (c) Tangential velocity, (d) Magnitude of the acceleration vector, (e) Angle between acceleration and radius.  

Solution.-

 
     
  [3] When the motor of a 34 cm diameter disk which is rotating at 180 rpm, is turned off, the disk gradually comes to rest in 18 s.  Determine: (a) angular acceleration of the disk. (b) Its average angular speed (c) Number of turns completed until the disk stops (d) Displacement of a point on the edge of the disk until this comes to stop.

Solution.-

 
 

 

Simulation module dealing with static friction in the Physics Virtual Lab.

The block on the gradually tilted plane remains there while the static friction is not overcome by the component of the weight opposing the friction.

PVL includes 200+  Physics Simulation Modules
  

 

 
 

[4] A 90-cm diameter wheel is rotating at 250 Rpm when the brakes are applied for 30 seconds and at the end of that time the wheel has reduced its velocity in 40%. Determine: (a) Acceleration experimented by the wheel (b) Number of turns completed during the time the brakes are applied (c) Distance covered by an edge point of the wheel during the time the brakes are applied.

Solution.-

 
 

 

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[5] A disk of 25 kg and 1.80 m in diameter is spinning at 5000 Rpm, when the engine that keeps it rotating is switched off. Before turn off engine, calculate: (a) speed of the disk. (b) Speed of a point on the edge of the disk. (c) The centripetal acceleration of a point on the edge of the disk. (d) If the disk stops 3 min after turning off the engine, calculate how many turns are completed in that time.

Solution.-

 
     
 

[6]  A 1.25m diameter disk that is at rest receives a constant acceleration of 0.40 rad/s2 during 5 minutes, and then the acceleration is turned off. Determine: (a) Number of turns completed during the 5 minutes (b) Maximum speed reached during the 5 min. (c) Time to stop after disconnecting the acceleration. (d) Number of turns completed after disconnecting the acceleration.

Solution.-

 
  [7] A 120 gr ball is tied to the end of a string of 3 m which is rotating with its other end fixed to a rotating shaft. The ball describes a circular orbit and moves with an acceleration of 10 m/s2 .  When the acceleration vector makes an angle of 25o  with rope, calculate (a) radial acceleration (b) tangential acceleration (c) speed of the ball.

Solution.-

 
     
 

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