http://tinypic.com/r/160v4nb/8 <<< image for all questions. 1. Fig.1 : The force
ID: 1768616 • Letter: H
Question
http://tinypic.com/r/160v4nb/8 <<< image for all questions.
1.
Fig.1 : The forces acting on the arm of a person lifting a dumbbell. The force F is the force puling on the hand due to the weight of the dumbbell, the force Warm is the weight of the arm and T is the tension due to the muscles connecting the arm and the trunk.
Question: Which of the three forces are contact forces?
T and Warm
Warm and F
T and F
Warm
all three forces
2.
Fig.1: The forces acting on the arm of a person lifting a dumbbell. The force F is the force pulling on the hand due to the weight of the dumbbell, the force Warm is the weight of the arm and T is the tension due to the muscles connecting the arm and the trunk.
Question: Due to Newton's third law we can make the following statement:
The weight of the arm has no reaction force.
The weight Warm is equal in magnitude to the tension T.
Forces Warm and T are a action/reaction pair of forces.
The arm exerts on the trunk a force which equals - T.
Forces Warm and F are a action/reaction pair of forces.
3.
Fig.1.The forces acting on the arm of a person lifting a dumbbell. The force F is the force pulling on the hand due to the weight of the dumbbell, the force Warm is the weight of the arm and T is the tension due to the muscles connecting the arm and the trunk.
Question: The dumbbell has a weight Wdumbbell. Why do we not include this force in the list of forces we consider in the text above for Fig. 1?
The force Wdumbbell acts in another direction than the listed forces and has therefore to be omitted.
We have already included the weight of the arm, Warm and there is no way to include two different weights in Newton's laws.
The force Wdumbbell has no reaction force in the figure, and for that reason cannot be considered in Newton's laws.
The force Wdumbbell does not act on the person's arm and has to be excluded when Newton's law is applied to the arm.
The dumbbell is not alive and can therefore not exert a force on another object.
4. http://tinypic.com/r/332mko3/8 <<<<< image for question 4
The figure above shows a standard man intending to do reverse curls in a gym. He holds his arms straight, using an overhand grip to hold the bar. If the mass of the bar is given as 136 kg, what is the tension in each of his shoulders? Consider the weight of the arm and the weight of the bar.
Not sure what the standard man arm weight is cant find it anywhere......
1.T and Warm
2.Warm and F
3.T and F
4.Warm
5.all three forces
Explanation / Answer
1. T and F
2. Forces Warm and T are a action/reaction pair of forces
3. The force Wdumbbell does not act on the person's arm and has to be excluded when Newton's law is applied to the arm.
4. the average weight of an arm of a healthy is considered to be 4.5 Kg.
now, as the mass of the bar is 136 kg it will exert an equal on both hands i.e. 68 kg .
now balancing the forces,
T = W+ F
T = (4.5+68)*9.8 = 710.5 N
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