Question

An observed and a vehicle, both starts moving together from rest with accelerations `5 m//s^(2)` and `2 m//s^(2)`, respectively. There is a `2 kg` block on the floor of the vehicle, and `mu = 0.3` between their surfaces. Find the work done by the running observer, during first `2` seconds of the motion.
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Answer 1

Correct Answer - 24 J
`FBD` of the block,

`f_(L) = 6N, F_("pseudo") = 4N`
:. `f = 4N`
acc. Of the block with respect to observes
`= 2-5 = -3 m//s^(2)`
`:.` Displacement of the block w.r.t. observes
`= (1)/(2) xx -3 xx 4 = -6 m`
`:.` work done by friction w.r.t. observers
`= -24 "Joule"`.