Question

A person is able to pull a rope with a force of 700 N. What is the minimum number of fixed and moveable pulleys that the person will require to lift up a 27,800 N elephant? Assume the pulleys themselves are weightless and the system has 100% efficiency.

A. 10 fixed, 10 moveable
B. 15 fixed, 15 moveable
C. 20 fixed, 20 moveable
D. 30 fixed, 30 moveable

Answer 1

C. 20fixed, 20moveables

Step-by-step explanation:

Efficiency of a machine = MA/VR × 100%

MA is the mechanical advantage

VR is the velocity ratio of the pulley

MA = Load/Effort

MA = 27,800N/700N

MA = 39.71

The velocity ratio formula depends on the type of machine. Since the machine in question is a block and tackle system, the velocity ratio will be the number of pulleys in the system.

Using the efficiency formula to get the VR

100 = 39.71/VR × 100

39.71/VR = 1

VR = 39.71

VR = 40(approximately)

This means that the minimum number of pulleys that the person will require to lift the load is 40pulleys i.e 20fixed, 20moveables

Answer 2

C option is correct

20 movable and 20 fixed pulleys required

Explanation:

To lift a 27,800 N elephant with a 700 N drive,

27800/700=39.7

the individual requires a mechanical favorable position of 39.7 which is equivalent to 40. A solitary movable pulley gives a mechanical favorable position of 2, two portable pulleys yield a mechanical preferred standpoint of 4, and a framework with three movable pulleys results in a mechanical favorable position of 6. In light of this example, 20 movable pulleys and 20 fixed are required to give a mechanical preferred standpoint of 40