Structures question

[confusedperson123]

(Heinemann 7.

A ladder of length 4.8m and mass 16kg is leaning against a wall so that it makes an angle of 65degrees to the horizontal. Calculate the magnitude of the torque exerted on the ladder (taken around where it contacts the ground) by each of the following forces:
1) weight of the ladder

Answer  = F×rsin = 160×2.4×sin25° = 160 N m

why do we use 25 instead of 65?

thanks

[superflya]

because u have to use the angle the ladder makes with wall not the horizontal.to find this angle: 180-65-90=25.

[median]

u can use cos65 instead.

[lachymm]

calculates the torque as F * distance = Torque

Therefore the sin(25) part is finding the horizontal distance. Draw a diagram of the ladder leaning on the wall and use SOHCAHTOA and you will realize why you use 25 degrees instead of 65 degrees.