A 720 N student stands in the middle of a frozen pond having a radius of 9.0 m.?

Question

He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 2.8 kg physics textbook horizontally toward the north shore at a speed of 5.0 m/s. How long does it take him to reach the south shore?

Answer 1

The student's mass is 720/9.8 = 73.5 kg (if you are given a different value for g, modify as required). By conservation of momentum, his initial velocity after throwing the book is (2.8)(5.0) / 73.5 = 0.19 m/s due south. Since there is no friction and no other acceleration, he will maintain this constant velocity and hence reach the shore in time t = d/v = 9.0/0.19 = 47 sec.