1.

A block is thrown with 14ms^(-1) over a long stationary plank as shown. Beofre the block comes at rest with respect to plank

Answer»

WORK done by kinetic FRICTION on the block be -180J
Work done by kinetic friction on the block will be 140J
Net work done by kinetic friction on the block plank system will be -180J
Net work done by kinetic friction on the block plank system will be +140J

Solution :`V_("rel")=U_("rel")+a_("rel")trArrt=2`
`V_("block")=14-5xx2=4`
`V_("block")=0+2xx2=4`
`W_("block")=-(1)/(2)xx2xx(14^(2)-4^(2))=-180J`
`W_("block")=(1)/(2)xx5xxu^(2)=40J`
`W_("system")=-140J`


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