Ramsay – A.P. Physics – Fall 2013 Spring Woods High School Name:______________________________________________________ Date: ___________ In-Class Examples – Circular Motion 4.11 The blade of a windshield wiper moves through an angle of 90 degrees in 0.28 seconds. The tip of the blade moves on the arc of a circle that has a radius of 0.76m. What is the magnitude of the centripetal acceleration of the tip of the blade? 4.12 What is the minimum coefficient of static friction necessary to allow a penny to ! rotate along a 33 ! rpm record (diameter = 0.300 m), when the penny is placed at the outer edge of the record? Unit 4: Dynamics Ramsay – A.P. Physics – Fall 2013 Spring Woods High School 4.14 A 75 g toy airplane is fastened to one end of a 44 cm string while the other end is held fixed at the ceiling. The plane whirls in a horizontal circle with an angle to the vertical of 30˚. a. What provides the centripetal force? b. Calculate the speed of the plane. (2.75 m/s) c. Calculate the tension of the string. (1.47 N) 4.13 a. A car makes a turn, what force is required to keep it in circular motion? b. A bucket of water is tied to a string and spun in a circle, what force is required to keep it in circular motion? c. The moon orbits the Earth, what force is required to keep it in circular motion? Unit 4: Dynamics Ramsay – A.P. Physics – Fall 2013 Spring Woods High School Name:______________________________________________________ Date: ___________ Practice – Circular Motion th Complete and submit scans (or pictures) of #4 through #7 in .pdf format to Canvas by Monday, Oct. 7 at 9:42am. 1. A 2 kg object is tied to a cord and swung in a horizontal circle of radius 1 m with a frequency of 80 rpm. Determine: a. The linear speed, (8.35 m/s) b. The centripetal acceleration, (69.8 m/s2) c. The centripetal force. (139.6 N) d. What happens if the cord breaks? Unit 4: Dynamics Ramsay – A.P. Physics – Fall 2013 Spring Woods High School 2. A 25 cm diameter record turns on a record player at 78 rpm. A bug rests on the record 2.5 cm from the outside edge. a. If the bug's mass is 0.01 kg, what force acts on him? (0.0667 N) b. What exerts this force? c. Where should the bug crawl if he wishes to reduce his force by one-half? (0.05 m) 3. a. What must the speed of a satellite be just above the surface of the earth if it is to travel in a circular orbit about the earth? (Rearth= 4000 mi, 1 mi = 1609 m) (7941.8 m/s) b. What is the nature of the centripetal force in this case? Unit 4: Dynamics Ramsay – A.P. Physics – Fall 2013 Spring Woods High School 4. An object of mass M on a string is whirled with increasing speed in a horizontal circle, as shown above. When the string breaks, the object has speed vo and the circular path has radius R and is a height h above the ground. Neglect air friction. a. Determine the following, expressing all answers in terms of h, vo, and g. i. The time required for the object to hit the ground after the string breaks. ( t = 2h / g ) ii. The horizontal distance the object travels from the time the string breaks until it hits the ground. ( x = v0 2h / g ) iii. The speed of the object just before it hits the ground.( vR = v02 + 2 gh ) (Careful, the question asks for resultant velocity not just vy) Unit 4: Dynamics Ramsay – A.P. Physics – Fall 2013 Spring Woods High School b. On the figure below, draw and label all the forces acting on the object when it is in the position shown in the diagram. . c. Determine the tension in the string just before the string breaks. Express your answer in terms of M, R, vo, and g. ⎛ v 4 ⎞ ⎜ FT = M g 2 + 02 ⎟ ⎜ R ⎟⎠ ⎝ Unit 4: Dynamics