A block of mass 25 kg is raised by a 50 kg man in two different ways as shown in Fig. 5.19. What is the action on the floor by the man in the two cases ? If the floor yields to a normal force of 700 N , which mode should the man adopt to lift the block without the floor yielding ?

Explanation

The FBD for the two cases is shown in fig.
In first case, let the force exerted by the man on the floor is `N_(1)`. We have
`N_(1)=T+50g`
Block is to be raised without acceleration, so
`T=25 g`
`:. N_(1)=25 g +50 g =75g = 75 xx 10`
`=750 N`
In second case, let the force exerted by the man on the floor is `N_(2)`. we have `N_(2)=50g-T and T=25g`
`:. N_(2)=50g-25g=25g=25xx10=250N`
As the floor yields to a downward force of 700 N, so the man should adopt the second case.