5. A 60-kg speed skater with a velocity of 18.0 m/s comes into a curve of 20-m radius. How much friction must be exerted between the skates and ice to negotiate the curve? How long does it take for her to complete a full revolution? (972 N, 6.98 s) 6. A 2.0-kg object is attached to a 1.5-m long string and swung in a vertical circle at a constant speed of 12 m/s. What is the tension in the string when the object is at the bottom of its path? What is the tension in the string when the object is at the top of its path? What is the minimum velocity of the object? (212 N, 172 N, 3.83 m/s) 7. It is found (through trial and error) that you will feel weightless when you travel at 24 m/s over a smoothly rounded hill. What is the radius of the hill? (58.78 m) 8. A 0.5 kg ball swinging in a horizontal circle at the end of a .78 m long string, causes the string to break when it is swung at 150 RPM. What was the maximum tension the string could withstand? (96.2 N) 8. In 1995, Cathy Marsal of France cycled 47.112 km in 1.00 hours. Calculate Marsal's centripetal acceleration. (The earth's radius is 6.38 E 6 m.) (2.68 x 105 m/s?)