Question

Two men of masses 60 kg and 80 kg are sitting at the ends of a boat of mass 60 kg and length 4 m
The boat is stationary. If the men now exchange their positions, then:Find the distance the boat moves and the movement of Center of Mass​

Answer 1

Explanation:

Initially centre of mass is at rest.

There is no external force on the system and hence no acceleration is produced.

So, centre of mass remains at rest .

Answer 2

The distance between boat and moment of centre of mass is 0.4 m

Explanation:

Given data:

• Masses = 60 Kg and 80 Kg
• Mass of boat = 60 Kg
• Length of boat = 4 m

Solution:

Let the centre of mass be = x

Now suppose the torque is at point x.

60 x = 60 ( 2 − x ) + 80 ( 4 − x)

60 x = 120 x − 60 x + 320 − 80 x

200 x = 440

x = 11 /  5

When positions are interchanged:

80 x = 60 (2 − x) + 60 ( 4 − x )

80 x = 120 − 60 x + 240 − 60 x

200 x = 360

x = 9 / 5

Now at centre of mass:

X ( shift) = 11/ 5 - 9/5 = 2 / 5

X ( shift) = 0.4 m

Hence the distance between boat and moment of centre of mass is 0.4 m

​