Question

a single fixed pulley and a movable pulley both are seprately used to lift a load of 50kg to the same height. Compare the efforts applied

Answer 1

Mechanical advantage (MA) given as,
MA =load(I)/effort(E)

The above equation indicates that Mechanical advantage and efforts are inversely proportional to each other.
The mechanical advantage of single fixed fully is 1.
For, single movable pulley, MA = 2
Load on both the pulleys =50 kgf
(see picture)

Hence, from the above,
In the case of single movable pulley,
MA > 1⇒ effort arm > load arm
and in the case of a single fixed pulley.
MA = 1⇒load arm = effort arm
∴ Effort applied in the single fixed pulley is less as compare single movable pulley.

Answer 2

Load to be lifted F

load

=50 kgf

Case 1 : Fixed pulley is used.

MA for single fixed pulley MA=1

Thus effort applied by the boy F

effort

=

MA

F

load

=

1

50

=50 Kgf

Case 2 : Movable pulley is used.

MA for movable pulley MA=2

Thus effort applied by the boy F

effort

=

MA

F

load

=

2

50

=25 Kgf

So, effort to be applied by the boy is less in case when he used a movable pulley because MA for a movable pulley is greater than 1.