A force of 10 N creates a displacement of 2 m but the work done on the body throughout its motion is equal to 70 J. What possibly can be the reason or this?
a) There are multiple forces action on the body
b) The body is at rest
c) The force is not uniform
d) The displacement is harmonic

Explanation

To reach minimum time he has to move with mximum possible acceleration.
Let the maxium accelerationis a
`:. Ma-muR=0rarrma=mu mg `
`rarr a=mug=0.9xx10=9m/s^2`
a. Initial velocity,
u=0 t=? `
a=9m/s^2 S=50m
From the equation `S=ut+(1/2)at^2`
`50=0+(1/2)9t^2`
`rarr t=10/3 sec`
b. After covering `50m`, velocity of teh athelete is given by `
v=u+at`
`=0+9xx(10/3)m/s `
He has to stop in minimum time. so deceleration is `-a=-9m/s^2(max)`
`R=mg
`ma=muR`
(maximum frictioN/Al force)
`rarr a=mug`
`rarr =9m/s^2 (deceleration)`
`u_1=30 m/s,v=0`
`rarr t=(v_1-u_1)/a`
`=(0-30)/(-a)`
`=(-30)/(-a) =10/3 sec`