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In the figure shown upper block is given...

In the figure shown upper block is given a velocity of `6 m//s` and lower block `3 m//s`. When relative motion between them is stopped.
.

A

Work done by friction on upper block is negative

B

Work done by friction on both blocks is positive

C

The magnitude of work done by friction on upper block is `10 J`

D

Net work done by friction is zero.

Text Solution

Verified by Experts

The correct Answer is:
A, C
From conservation of linear momentum `(1+2) v = (6 xx 1)+(2-3)`
`:. v = 4m//s` (of both the blocks)
from work energy theorm
i.e., `W_("total") = Delta KE` on `1 kg` block,
`W_(f) = (1)/(2) xx 1 xx (4^(2) - 6^(2)) = - 10 J`
on `2 kg` block `W_(f) = (1)/(2) xx 2(4^(2) - 3^(2)) = + 7 J`
`:.` Net work done by friction is ` - 3 J`.
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