Aperson 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

C. 20fixed, 20moveables

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

d₁ = displacement of tern from arctic to antarctic = 11000 miles

d₂ = displacement of tern from antarctic to arctic =   - 11000 miles

d = total displacement for the journey

total displacement for the journey is given as

d = d₁ + d₂

d = 11000 + (-11000)

d = 0 miles

t₁ = time of travel from arctic to antarctic = 3 months = 3 x 30 days = 90 days

t₂ = time of travel from antarctic to arctic = 3 months = 3 x 30 days = 90 days

t = total time of travel

total time of travel is given as

t = t₁ + t₂

t = 90 + 90

t = 180 days

average velocity is given as

average velocity = total displacement/ total time

v = d/t

v = 0/180

v = 0 miles/day

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s