NEET-XII-Physics
08: Work and Energy
- #8A small block of mass m is kept on a rough inclined surface of inclination θ fixed in an elevator. the elevator goes up with a uniform velocity v and the block does not slide on the wedge. The work done by the force of friction on the block in time t will be
(a) zero
(b) mgvt cos2θ
(c) mgvt sin2θ
(d) mgvt sin 2θdigAnsr: cAns : c.(c) mgvt sin2θ
Distance (d) travelled by the elevator in time t = vt
The block is not sliding on the wedge.
Then friction force (f) = mg sin`` \theta ``
Work done by the friction force on the block in time t is given by
`` W=Fd\,\mathrm{\,cos\,}(90-\theta )``
`` \Rightarrow W=mg\,\mathrm{\,sin\,}\theta \times d\times \,\mathrm{\,cos\,}(90-\theta )``
`` \Rightarrow W=mgd{\,\mathrm{\,sin\,}}^{2}\theta ``
`` \therefore W=mgvt{\,\mathrm{\,sin\,}}^{2}\theta ``
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