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The whole force analysis method of high school physics How to use it
Take several objects as a whole. Then the interaction force between these objects can not be calculated. When accepting the analysis, only the force exerted on the whole by other objects is analyzed. For example, when a person sits on the chair of the bus, the chair is fixed on the bus. By using the whole analysis, the force exerted on the whole of the bus is gravity, the support force and friction force of the ground, We don't consider the interaction between people, chairs and buses
As shown in the figure, object a is leaning against a smooth vertical wall and supported by a hinged rod. The gravity of object a is g, the gravity of rod is g ˊ, and the angle between rod and vertical direction is a, then ()
A. The resultant force direction of the elastic force and friction force of the object a to the rod end must be along the direction of the rod B. the elastic force of the object to the rod will decrease with the increase of the gravity g of the object C. if the hinge position is moved to increase the angle a, but the object a is still supported, the elastic force of the object to the rod will increase D. if the gravity g ˊ of the rod is increased, the friction force of the object a to the rod will increase
A. The force analysis of a is as shown in the figure; the object is in balance due to gravity, the elastic force of the rod, the supporting force of the wall and the friction force; therefore, the resultant force of several forces must be zero; therefore, the friction force of the rod to the object and the elastic force of the rod to the object should be greatly reversed with the resultant force of other forces, so it can not be along the direction of the rod; therefore, a is wrong; B, increase
As shown in the figure, the two ends of the light rope are respectively connected with objects a and C, Ma = 1kg, MB = 2kg, MC = 3kg. The dynamic friction coefficient between objects a, B, C and C and the ground is μ = 0.1, and the friction between the light rope and pulley can be ignored. If Object C is to be pulled by force, the minimum horizontal left pulling force on Object C is (g = 10m / S2) ()
A. 6NB. 8NC. 10ND. 12N
First of all, because a and C are connected by light ropes, they have the same speed at all times; while B is subject to the friction of a and C respectively, and the friction that C can provide is greater than that a can provide, so object B must move with C. Therefore, we find that B and C are relatively static, and can be regarded as an object, BC as a whole
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