## anonymous one year ago a worker uses a block and tackle with a mechanical advantage of 1.74 to lift a 225 N crate a distance of 16.5 m. He pulls 33.0 m of rope. What force did she use to lift the crate? 29.0 N , 129 N , 57.0 N , or 392 N

1. Michele_Laino

please, wait a moment a student asked me for help in Mathematics

2. anonymous

ok!

3. Michele_Laino

here we have to consider the work done by the weight force of the crate, which is: ${W_1} = Fs = 225 \times 16.5 = ...$

4. Michele_Laino

what do you get?

5. anonymous

i get 3712.5

6. anonymous

is that right?

7. Michele_Laino

ok! that's right!

8. anonymous

what happens next? to find the solution to the problem?

9. Michele_Laino

next we have to consider the work W_2 done by the worker, which is: ${W_2} = Rd$ Now we don't know what is R

10. Michele_Laino

whereas d=330 meters

11. Michele_Laino

oops..d=33 meters

12. anonymous

ok!

13. Michele_Laino

in order to find the value of the requasted force R, we have to apply this condition: $\Large 1.74 = \frac{{3712.5}}{{33R}}$ so what is R?

14. anonymous

64.655?

15. Michele_Laino

sorry, it is the wrong result, please wait, I revise my reasoning

16. anonymous

ok!

17. Michele_Laino

the requested force is given by the subsequent simple computation: $1.74 = \frac{R}{F},\quad R = 1.74F = 1.74 \times 225 = ...Newtons$ here I have applied the definition, of advantage of a simple machine, namely: ${\text{advantage}} = \frac{{{\text{resistive force}}}}{{{\text{agent force}}}}$

18. anonymous

391.5? so our solution is 392 N?

19. Michele_Laino

yes! that's right!

20. anonymous

yay!

21. Michele_Laino

:)