A small shelf bracket is designed to hold 80 N as shown. It is supported by a sc

Question

A small shelf bracket is designed to hold 80 N as shown. It is supported by a screw is attached to the wall. Take the pivot point to be the bottom point of the bracket, and assume the bracket is slightly loose, so that it only touches the wall at the bottom. How much torque about is exerted by the 80 N load? 80 N cm 400 N cm 480 N cm 720 Ncm 823 N cm What is the minimum horizontal force exerted by the screw to hold the bracket on the wall? 67 N 80 N 96 N 144 N 137 N If a 20 kg mass is hung from the cable configuration shown, what is the tension T_2 in the horizontal string? 113 N 196 N 226 N 339 N 392 N If a ladder is leaning against a frictionless wall, and the floor has a coefficient of friction of only 0.2, what angle must the ladder make with the floor to keep from slipping? 0 degree 51 degree 68 degree 78 degree 84 degree

Explanation / Answer

25) b) 400 N.cm

Torque = r*F*sin(theta)

= 5*80*sin(90)

= 400 N.cm

26) a) 67 N

Apply net torque about bottom = 0

80*5 - F*6 = 0

==> F = 80*5/6

= 67 N

27) a) 113 N

T3 = 20*9.8 = 196 N

T1*sin(60) = T3

T1*cos(60) = T2

tan(60) = T3/T2

==> T2 = T3/tan(60)

= 196/tan(60)

= 113 N

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