A man weighing 80 kg is standing at the centre of aflat boat and he is

1.	A man weighing 80 kg is standing at the centre of aflat boat and he is 20 m from the shore. He walks 8m on the boat towards the shore and then haltsThe boat weight 200 kg. How far is he from theshore at the end of this time?(A) 11.2 m(C) 14.3 m(B) 13.8 m(D) 15.4 m
Answer» As you can see there is no net displacement of centre of mass of the whole system as the boy moves toward the shore boat moves to the opposite side to balance the centre of mass. Say that the boat moves by distance x away from the shore therefore boy moves x-8 as you can see there is no net external force delta x of centre of mass is zero therefore, M1 X1 + M2X2 = 0 200(x) + 80(x-8) = 0 280x = 640 x = 2.3 Therefore boy moves 8-2.3 = 5.7 towards the shore Now the total distance between the shore and the boy is 20 - 5.7 = 14.3

A man weighing 80 kg is standing at the centre of aflat boat and he is 20 m from the shore. He walks 8m on the boat towards the shore and then haltsThe boat weight 200 kg. How far is he from theshore at the end of this time?(A) 11.2 m(C) 14.3 m(B) 13.8 m(D) 15.4 m

Answer»

As you can see there is no net displacement of centre of mass of the whole system as the boy moves toward the shore boat moves to the opposite side to balance the centre of mass.

Say that the boat moves by distance x away from the shore therefore boy moves x-8

as you can see there is no net external force delta x of centre of mass is zero therefore,

M1 X1 + M2X2 = 0 200(x) + 80(x-8) = 0

280x = 640 x = 2.3

Therefore boy moves 8-2.3 = 5.7 towards the shore

Now the total distance between the shore and the boy is 20 - 5.7 = 14.3

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