Rescue?. Your friend (mass 65.0 kg) is standing on the ice in the middle of a frozen pond There is very little friction between her feet and the ice, so she is unable to walk. Fortunately, a light rope is tied around her waist and you stand on the bank holding the other end. You pull on the rope for 3.00 s and accelerate your friend from rest to a speed of 6.00 m/s while you remain at rest. What is the average power supplied by the force you applied?

Solution 90P Step 1: Her mass is 65 kg. Initially she was at rest and by pulling her final velocity reached to 6 m/s. The change in kinetic energy is, K.E = K.E K.E final initial 2 2 = 1/2 × m × (V f V i 2 = 1/2 × 65 × (6 0) = 0.5 × 65 × 36 = 1170 J . Step 2: We know from work energy theorem that, Work done is equal to the change in kinetic energy. So, the work done during the process is 1170 joules.