a. The Earth orbiting the Sun
b. A car making a curve on a horizontal road
c. A ball on a string swinging in circles on a horizontal surface
d. A ball on a string swinging in circles in the vertical plane:
– at the top of the circle
– at the bottom of the circle
e. A ball on a string swung in circles in a horizontal plane in mid-air such that the plane of the circle is below the end of the string held at the centre of the circle.
f. A pilot in a plane making a vertical circle in mid-air:
– at the top of the loop (she is upside down at this position, as is the plane)
– at the bottom of the loop
2. Sometimes road surfaces have banked curves. Explain how this helps cars make turns more safely. Include a free-body diagram.
3. A rock of mass 200 g is attached to a 0.75 m long string and swung in a vertical plane.
a. What is the slowest speed that the rock can travel and still maintain a circular path?
b. What is the tension in the string at the bottom of the swing?
4. Kim has her coffee cup on her car’s dash when she takes a corner with radius 4 m at 20 km/h. What is the minimum coefficient of static friction which would
allow the coffee cup to stay there without slipping?
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