Topic content:
Two small balls A and B, both of which have a mass of m and can be regarded as particles, hang them at the same point with two thin wires of equal length, connect them with thin wires of equal length, and then apply a horizontal force on small ball B. At this time, the three thin wires are in a straight state, and the O A rope is just in the vertical direction, and small balls A and B are still, then the horizontal force F is
Best answer:
Answer analysis:
It can be seen from the state of A that A is under gravity and vertical upward tension, and there is no tension in rope AB
B Under gravity, tension T and horizontal tension F of rope OB are balanced according to the copoint force:
Tcos60°=mg
Tsin60°=F
Simultaneous solution: F=
Test core:
force analysis:
1. Methods of force analysis of objects ① Methods: overall method, isolation method.
② Choice: When the physical problem involved is the interaction between the whole and the outside world, the application of the overall analysis method does not need to consider the role of internal forces; When the physical problem involved is the interaction between objects, the isolation analysis method should be applied, and then the internal force of interaction in the original whole will become the external force of each independent object.
2. The sequence of force analysis: first gravity, then contact force, and finally other external forces.
3. Problems that should be paid attention to in force analysis ① When analyzing the force on the object, only the force exerted by the surrounding objects on the research object is analyzed;
② During force analysis, do not apply too much force or omit force. Pay attention to determining the strength object and force bearing object of each force. In the synthesis and decomposition of force, do not regard the actual non-existent resultant force or component force as the force applied to the object;
③ If the direction of a force is difficult to determine, it can be analyzed by hypothesis method;
④ The force condition of the object will change with the change of the motion state, and it can be determined by calculation according to the learned knowledge when necessary;
⑤ The external effect of force analysis should be considered as a whole, and the interaction should be isolated.