13. Buddy the Elf has a toy airplane (m = 0.5 kg) on a string that he whirls around his head in a circle at a constant speed of 10 m/s. The circle is 80 cm in radius and is perfectly parallel to the ground. The figure to the right shows a top-down view of the situation. How much work does the force of tension do on the airplane to keep it moving in a circular path? a) W = 0 J b) W=62.5 J c) W = 25 J d) W = 2.5 J Buddy Y = 10 m/s r = 80cm