A junior high school physics problem, please do me a favor

1) If this ammeter is directly connected to the circuit, what is the maximum voltage allowed between the two binding posts of the ammeter?

The maximum permissible voltage v=i*r==v

2) As shown in Figure B, if the ammeter is connected in parallel with a fixed-value resistor R, so that the current through g is 6mA, the total current between A and B is equal, so that between A and B (in the dotted box) is equivalent to an ammeter with a range of 0 (Fig. C), and the size of the fixed-value resistor R connected in parallel is obtained

When the current through G is 6mA, the voltage at both ends of the ammeter G is V=I*R==V

According to the relationship that the voltage of the parallel circuit is equal, the voltage at both ends of the unknown resistor r is also V, and the current flowing through R is i= = a

So, the resistance of the unknown resistor r = u i = v a = ohms.

Answer: The fixed-value resistor r for parallel connection is ohms.

1)u=i*rg=6*

2) From (1), it can be seen that the voltage at both ends is;

The ammeter is connected in parallel with the resistor, so the current passing through the resistor ir=r=

The stiffness coefficient of the b spring is inversely proportional to the length of the spring, so with a broken section, its stiffness coefficient will become larger, for the same weight, the measured deformation will be less than the true value, and the reading indicator will be less than the real value.

Analysis: If the inclined plane is smooth, then f 15n 5n 10n When the object is stationary on the inclined plane, the force must be balanced, which can be considered in three cases:

1. There is no sliding tendency on the relative inclined plane of the object, at this time f 10N2, the relative inclined plane of the object has a downward sliding tendency, and the maximum tensile force is f' f f 10n 5n 5n

3. The object has an upward sliding tendency relative to the inclined plane, and the maximum tensile force is f" f f 10n 5n 15n

The option is b c d

Uniform linear motion and rest are both states of equilibrium.

Therefore, if the force of 15N makes it move at a uniform speed, then let it be stationary, which is also the force selection b of 15N

Test Topic: Application of the Two-Force Equilibrium Condition

Analysis: Find the component of gravity along the inclined surface according to the upward motion of the object at a uniform motion, then find the maximum and minimum values of the tensile force when the object is at rest, determine the range of the tensile force that makes the object rest, and then select the answer according to the range

Answer: Solution: The object moves upward with a uniform velocity on the inclined plane, and in the direction parallel to the inclined plane, the object is subjected to the tensile force f parallel to the upward inclined plane, the frictional force ff parallel to the downward inclined plane, and the component force g1 of the gravitational force parallel to the downward inclined plane

The object is in equilibrium and the net force in the direction parallel to the inclined plane is zero, i.e.: f-ff-g1=0, g1=f-ff=15-5=10 Newtons

Here the maximum static friction experienced by the object is equal to the sliding friction, i.e. the maximum static friction ffmax = 5 Newtons Because the maximum static friction ffmax is less than the component of gravity g1, in order for the object to rest on the inclined plane, the tensile force must be parallel to the inclined plane

1) When the tensile force is large, the friction force is parallel to the inclined downward surface, when the friction force is the maximum static friction force, the tensile force is the maximum, let the maximum tensile force be f1, and the equilibrium condition is obtained: g1+ffmax-f1=0, f1=g1+ffmax=15 Newtons

2) When the tensile force is small, the friction force is parallel to the inclined plane, when the friction force is equal to the maximum static friction force, the tensile force is the smallest, let the minimum tensile force be f2, and the equilibrium condition is obtained: f2+ffmax-g1=0, f2=g1-ffmax=10-5=5 Newtons

When the object is at rest on an inclined plane, the range of tensile force is 5 Newtons f 15 Newtons

2o Newton is not in the range of tensile force, so A is false 15 Newton, 10 Newton, 5 Newton are all in the range of tensile force, so BCD is correct

Therefore, BCD comments: This question examines the equilibrium conditions of the object, force analysis, where the magnitude and direction of friction force change with the change of tensile force, and need to be discussed according to the magnitude of tensile force, and the test question is more difficult The key to solving this question is to correctly carry out force analysis, and then solve it by the equation of the equilibrium condition column

c。Because the two forces are balanced in the same plane, that is to say, the object in the straight line where the two forces are located will remain at rest or in a constant motion, the title does not say that it takes 15n to move upwards to have a uniform velocity, then the rest also needs 15n, but the friction force can be at least consistent with 5n, so it still needs 10n to balance and keep it at rest. Of course, don't think about the difference between sliding friction and static friction in junior high school now.

There is no picture, but it seems that it is best to choose D

Analysis: a: Because of the level of the holder, the gravity of the ball is balanced with the support force of the holder; If the ball is subjected to friction (static), which force balances it?

Therefore, there is no friction between the ball and the holder;

b: The gravity of the ball and the support force of the ball support to it are a pair of equilibrium forces, the balance force refers to the force on the same object, and the pressure is the force exerted by the ball to the ball holder, which is obviously wrong;

C: After the ball flies out, the cue stick has no force on the ball, and it is impossible to do work! It can only be said that the club does work on the ball at the moment of hitting the ball;

d: For the actual situation, due to the presence of air resistance, the mechanical energy will be reduced and converted into the internal energy generated by friction; But if air resistance is not taken into account, mechanical energy is conserved! This choice seems a bit problematic, right?

Hope it helps...