Question

One end of uniform stretcher is to be lifted from floor so that the other end may be considered to be the pivot point. The stretcher is 2m long and its mass is 20kg .how much force to lift your end, what is the mechanical advantage?

Answer 1

Force required to lift = force at pivot `= 98`N
Mechanical advantage = 2

Explanation:

At the moment that the stretcher is first lifted it is supported only at each end and it is still horizontal.

Because it is uniform, the mass is evenly distributed. If it is horizontal the force due to gravity is supported equally at each end.
The center of mass is at the mid point of the stretcher.

The total force due to gravity is

`F = ma = 20 * 9.8 = 196`N

Force required to lift`= 196/2 = 98N =`force at pivot (when horizontal)

The mechanical advantage
`= F_"load"/F_"applied"`

`= (196N)/(98N)`

`= 2`

Note: the distribution of lifting force between ends changes as the angle increases above horizontal.