Torque - Sign - AP Physics B

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

t_net =

= .30 m(50. N) - .50 m(50. N)sin120°

- 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

F_wally F_wallx

_{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 F_wally & F_wallx

Force of beam on wall = Wall force on beam

Tcosq = F_wallx

=794 Ncos30

F_wallx= 687 N

II. Find F_wally

SF_y = 0

mg + Mg = F_wally+ Tsin30

F_wally = 123 N

Giancoli - p. 248) 18, 20, 21