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8.2. A metal bar hangs loosely from a pivot on the ceiling. A parent pushes on the bar with a force F₁ horizontally at a distance y₁ = 0.6 m below the ceiling. Their child pushes near the bottom of the bar in the opposite direction, applying a force F₂ = 35 N at a point y₁ = 1.1 m below where their parent is pushing. (a) How hard does the parent have to push to keep the bar from moving? (b) What is the magnitude and direction of the net force on the pivot point if the mass of the bar is 1.8 kg? F2 Y1 Y2 F₁

8.2. A metal bar hangs loosely from a pivot on the ceiling. A parent pushes on the bar with a force F₁ horizontally at a distance y₁ = 0.6 m below the ceiling. Their child pushes near the bottom of the bar in the opposite direction, applying a force F₂ = 35 N at a point y₁ = 1.1 m below where their parent is pushing. (a) How hard does the parent have to push to keep the bar from moving? (b) What is the magnitude and direction of the net force on the pivot point if the mass of the bar is 1.8 kg? F2 Y1 Y2 F₁

College Physics
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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8.1. A meter stick balances on a knife edge be- low the 50 cm mark. When two nickels are stacked and centered on the 12 cm mark, the whole system is now found to balance when supported at the 45 cm mark. If a nickel has a mass of 5.0 g, what is the mass of the meter stick? 8.2. A metal bar hangs loosely from a pivot on the ceiling. A parent pushes on the bar with a force F₁ horizontally at a distance Y₁ = 0.6 m below the ceiling. Their child pushes near the bottom of the bar in the opposite direction, applying a force F2 35 N at a point y₁ = 1.1 m below where their parent is pushing. (a) How hard does the parent have to push to keep the bar from moving? (b) What is the magnitude and direction of the net force on the pivot point if the mass of the bar is 1.8 kg? F₂ Y1 Y2 F₁ 8.3. A diver has a mass of 70 kg. In 'tuck' position, we can treat this mass as a disc of radius 0.50 m, but when fully extended, the diver is more like a rod of length 2.4 m. 8.4. The bicep muscle pulls on the bones of the forearm at a fairly short distance from the elbow, which acts as a pivot point. An object is held motionless in the hand at an angle 60° to the bicep which is aligned vertically, as shown in the figure to the right. The bicep must exert a force to keep everything in equilibrium. (a) Compare the rotational inertia of this diver in tuck position to their rotational inertia when fully extended. (b) If this diver ends their dive fully extended and is rotating at 0.85 rotations/s, what was their rotational speed earlier in the dive when they were in tuck position? (c) Does the transition from tuck to fully extended require extra energy to be provided by the diver's muscles? (a) What torque does a 5.0 kg object create relative to the elbow if the distance from the elbow to the center of the hand is 35.0 cm? (b) If the forearm itself has a mass of 2.0 kg and a center of mass that is 16 cm from the elbow, what torque does that create relative to the elbow? (c) What force must the bicep exert to keep things in equilibrium if the distance from the elbow to the point of attachment for the bicep is 4.0 cm along the forearm? (d) What is the magnitude of the force of compression in the elbow joint?
Transcribed Image Text:8.1. A meter stick balances on a knife edge be- low the 50 cm mark. When two nickels are stacked and centered on the 12 cm mark, the whole system is now found to balance when supported at the 45 cm mark. If a nickel has a mass of 5.0 g, what is the mass of the meter stick? 8.2. A metal bar hangs loosely from a pivot on the ceiling. A parent pushes on the bar with a force F₁ horizontally at a distance Y₁ = 0.6 m below the ceiling. Their child pushes near the bottom of the bar in the opposite direction, applying a force F2 35 N at a point y₁ = 1.1 m below where their parent is pushing. (a) How hard does the parent have to push to keep the bar from moving? (b) What is the magnitude and direction of the net force on the pivot point if the mass of the bar is 1.8 kg? F₂ Y1 Y2 F₁ 8.3. A diver has a mass of 70 kg. In 'tuck' position, we can treat this mass as a disc of radius 0.50 m, but when fully extended, the diver is more like a rod of length 2.4 m. 8.4. The bicep muscle pulls on the bones of the forearm at a fairly short distance from the elbow, which acts as a pivot point. An object is held motionless in the hand at an angle 60° to the bicep which is aligned vertically, as shown in the figure to the right. The bicep must exert a force to keep everything in equilibrium. (a) Compare the rotational inertia of this diver in tuck position to their rotational inertia when fully extended. (b) If this diver ends their dive fully extended and is rotating at 0.85 rotations/s, what was their rotational speed earlier in the dive when they were in tuck position? (c) Does the transition from tuck to fully extended require extra energy to be provided by the diver's muscles? (a) What torque does a 5.0 kg object create relative to the elbow if the distance from the elbow to the center of the hand is 35.0 cm? (b) If the forearm itself has a mass of 2.0 kg and a center of mass that is 16 cm from the elbow, what torque does that create relative to the elbow? (c) What force must the bicep exert to keep things in equilibrium if the distance from the elbow to the point of attachment for the bicep is 4.0 cm along the forearm? (d) What is the magnitude of the force of compression in the elbow joint?
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