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Unformatted text preview: Assignment 11 1. Three systems in static equilibrium. a. A mobile hangs as shown. The strings and crossbars are massless. The strings supporting the crossbars are attached at distance /4 from the left end. The mass of ball #1 is m . What are the masses of the other balls? b. A large ball of mass M is attached to a string attached to a frictionless vertical wall as shown. The ball has radius R and the distance d shown is between the point where the string is attached to the wall and where the ball touches the wall. Find the tension T in the string and the normal force N exerted on the ball by the wall. Ans : T = mg 1 + ( R / d ) 2 , N = mg ( R / d ) . c. Shown is a diagram of the foot of a person supporting her weight on the ball of one foot, with the heel slightly off the oor. The ball is a . The leg bone b is attached to the foot at horizontal distance 15 cm from a , and the calf muscle c acts at horizontal distance 20 cm from a . The persons weight is 500 N. What vertical forces (magnitude and direction) act at b and c ? Ans : At b , 2000 N down; at c , 1500 N up. 2. How and how not to get a wheel over a curb. The wheel of a babys stroller needs to be lifted over a curb, as shown. Force F is applied at the axle of the wheel, at angle above the horizontal. The wheel has mass M and radius R ....
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