Question

You are a disgruntled physics student (730N) standing in the middle of a frozen pond of radius 10m. Since the pond is frozen you can't move due to lack of friction. Being disgruntled you decide to throw your ever present physics book m=1.2kg horizontals with a speed of 5m/s. How long does it you to reach the bank?  

Answer 1

law of conservation of momentum:

initial momentum of the man + initial momentum of book = final mom.of man + final mom. of book

mass _man * u _man +mass _book * u _book = mass _man *v _man + mass _book * v _book

(730/9.81) * 0 + 1.2 * 0 = (730 / 9.8) * v _man + 1.2* 5

0 =  74.4138 * v _man + 6

v _man = - 6 / 74.4138

v _man = - 0.08063 m/s.

Therefore,

the time taken,

t = distance / speed  

( where the distance = the radius of the pond and we take -ive because we have been considering the direction of motion of the book to be positive and hence the opposite direction(in which the man moves) is negative.)

t = - 10 / -0.08063

t ~ 124.023 s,