Two men to masses `80kg` and `60kg` are standing on a wood plank of mass `100kg`, that has been placed over a smooth surface. If both the men start moving towards each other with speeds `1m//s` and `2 m//s` respectively then find the velocity of the plank by which it starts moving.

Answer

`-(1)/(6) m//sec.`

Explanation

Applying momentum conservation `,`
`(80)1+60(-2)=(80+60+100)v`
`v=(-40)/(240)=-(1)/(6)m//sec.`