124s08-exam1

# Which of the following is true if there is static

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4. Which of the following is true if there is static equilibrium? a) The sum of all frictional forces is 0. b) The sum of all torques is 0, but only about the center of mass. c) The sum of all torques is 0. d) Each force has to point directly towards the center of mass. e) Each force applied has to create a non-zero torque about the center of mass.

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5. A uniform 2 m long rod has mass 2 kg. Attached to it is a small 0.5 kg mass at the left end, and a small 0.75 kg mass at the right end. How far from the left end of the stick is the center of gravity of the system? 6. A shelf of mass 5 kg sticks out 50 cm from a wall. It is supported by a cable, attached to the outer edge of the shelf and to the ceiling directly above. A small 2 kg mass sits at the center of the shelf. What is the tension in the cable? 7. A 0.5 mm radius steel wire, with Young’s modulus 2 × 10 11 Pa, supports a 7 kg mass. When not stretched, the wire is 2.4 m long. What is the strain?
8. Three identical 1000 kg masses sit at on three corners of a square, with sides 1 m long. What is the magnitude of the total gravitational force on mass B, from masses A and C? a) 6.67 × 10 5 N b) 1.33 × 10 4 N c) 9.43 × 10 5 N d) 8.90 × 10 9 N e) 0 N - the forces are in different direc- tions and cancel 9. Your weight on the earth is 600 N. On the moon, your weight is 100 N. The diameter of the moon is 3500 km. What is the mass of the moon?

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