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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: confusedperson123 on March 20, 2010, 09:33:54 am

Title: Structures question
Post by: confusedperson123 on March 20, 2010, 09:33:54 am: (Heinemann 7.8)

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
Title: Re: Structures question
Post by: superflya on March 20, 2010, 10:58:14 pm: because u have to use the angle the ladder makes with wall not the horizontal.to find this angle: 180-65-90=25.
Title: Re: Structures question
Post by: median on May 27, 2010, 07:40:17 pm: u can use cos65 instead.
Title: Re: Structures question
Post by: lachymm on May 28, 2010, 04:38:24 pm: $F*Sin(25)$ 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.