Ex) Compound Wheel

Find Net Torque, Both F =50. N

r1 = 30 cm, r2 = 50 cm

A 30 cm disk and a 50. cm disk are attached to an axle that passes through their centers.

If a 50. N force hangs from the 30. cm disk and a  50. N force is applied to the 50. cm disk a shown above what is the net torque on the compound wheel

CW  negative

CCW positive

 

tnet =

= .30 m(50. N) - .50 m(50. N)cos120°

 

 

- 6.7 mN

 

Ex 2) A 2.20 m uniform beam with a mass of 25.0 kg has a 28.0 kg sign attached to it.

Find all the forces on the beam

Find the tension on the cable T and the components of wall's force on the beam 

Fwally  Fwallx

 

I. Finding Cable Tension

 St = 0

TsinqL = mgL/2+MgL

 

Tsinq = mg/2+Mg

 

Tsin30 = mg/2+Mg

 

T/2 = mg/2+Mg

 

Ex 2) A 2.20 m uniform beam with a mass of 25.0 kg has a 28.0 kg sign attached to it.

 

T = mg + 2Mg

 = 25.0 kg(9.8 m/s2)+ 2(28.0 kg)(9.8 m/s2)

 

 

T = 794 N

II. Find Fwally & Fwallx

 

 

 

Force of beam on wall = Wall force on beam

Tcosq = Fwallx

 

 =794 Ncos30

 

Fwallx = 687 N

 

 

 

 

II. Find Fwally

SFy = 0

 

mg + Mg = Fwally + Tsin30

 

 

 

Fwally = 123 N

 

 

 

Giancoli - p. 248) 18, 20, 21

 

 

 

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