An athlete initially at rest (at t =0) starts running and reaches his peak speed at (t = 5s) (on a
horizontal road). The work done by friction on the athlete during t = 0 and t = 5s in,
(A) Positive
(BL Negative (C) Zero
(D) None of these
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Answer:
Negative
Explanation:
The athlete's displacement is in forward direction but the frictional force always acts in the direction opposite to the motion. Hence,
W=F.s
W=F*s cos©
W=F*s cos 180°
W=F*s (-1)
W=-F*s
W=-ve
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