Mechanics and physics questions in high school and physics and mechanics in high school

When at rest, object A is subjected to the spring tension force F1 to the right, magnitude 5N, and friction force F2 to the left, magnitude 5N.

When accelerating the motion, if A is still stationary, then the tensile force F1 is applied'Constant, 5n to the right, is not enough to provide an acceleration of 1m s 2 for object a, then the frictional force f2'Change direction, to the right, max 5N, F1'+F2'=10n, which just provides the acceleration of object A by 1m s 2, so object A can just remain stationary.

If here the acceleration requires a pulling force between 0 and 5n, then f2 does not change direction, just decreases.

If here the acceleration requires a pulling force between 5 and 10N, then F2 changes direction and the magnitude is from 0 to 5N.

If the acceleration requires a tensile force of more than 10N, then F2 changes direction to a maximum of 5N, and the spring is elongated, and F1 increases to meet this acceleration requirement.

So the answer is a.

Reason for choosing a, when the car is not moving, the static friction of the object at this time = 5n, you can know that the static friction of the object is greater than or equal to 5n When the car moves to the right at 1m s2, it has not exceeded its maximum static friction at this time, so the object is fast and the car is stationary. So everything else is wrong ...

The friction should be unchanged, the elasticity should be increased, and the overall thinking should be used. The block has an acceleration to the right, indicating that the combined force is to the right. So the force exerted by the spring on the object is greater than the frictional force.

According to f=u mg, the frictional force is constant. So it's an increase in elasticity. Since f=kx, the spring is elongated and the object moves to the left relative to the trolley.

That's right. Horizontal ff=macOS30°

The vertical direction is f—mg=masin30°

Known f(6 5) mg

The simultaneous solution yields ff=(3 5)mg

The answer is right, the upward acceleration of the person is provided by the resultant force, and the direction of the resultant force is the direction of the elevator, then the resultant force can be decomposed into horizontal and vertical directions, and the force in the vertical direction is, according to the included angle, it can be known that the force in the vertical direction: the force in the horizontal direction = tan30 ° so you can find the force in the horizontal direction =

In the end, the answer is right.

To put it simply, it can be done as follows: (6 5mg-mg) * cot30 = mg 5 * 3 = 3 5mg

That's right! a can be understood as acceleration without the gravitational pull of the Earth. After that, the second step of the line is to subtract the influence of the earth's gravity, and the rest is the acceleration given by the elevator!

The answer is correct: Man is subjected to three forces: friction is horizontal to the left, gravity is vertically downward, support is vertically upward, support is greater than friction, the resultant force is upward along the inclined plane, and the acceleration is decomposed on the x-axis and y-axis through orthogonal decomposition, then fx=ff=ma x fy=fn-mg=ma y on the y-axis, and then fn= gets ff= ok?!Satisfied?

That's right!

The direction of acceleration is the same as the direction of the resultant force, and the resultant force of gravity, support force, and friction force is along the direction of the elevator, that is, the direction of acceleration.

1. 1

2.From x=1 2*a*t 2, a=(2x) t 2 a= t=4 v=6, average v=3

3.To know that the time is the same, set the height of the tower x then x-7=1 2gt 2

v = root number 2gx x-1 = root number 2gx * t+1 2gt 2 can be obtained t = three-fifths of the root number five x=16

The unit is too much trouble.

Looking at it, I went back to my high school days and slept all day, haha.

1.First, using the integral method, the three iron blocks of a, b, and c are regarded as a whole, then the pressure of this whole on the ground f [total] = GA+GB+GC=210N, and only A and B touch the ground, and A, B, and C are symmetrical.

It is easy to conclude that the pressure of iron block A on the ground fn=f [total] 2=105n2For C, because the inclined plane is smooth, the pressure of the iron block C on A and B is perpendicular to the inclined plane, then C is balanced by the gravity of the horizontal and vertical downward, the pressure of A to C perpendicular to the contact surface and the pressure of B to C perpendicular to the contact surface, and the pressure of C to A is easily solved by doing the force analysis diagram N[A C]=5 2

3.The force analysis diagram of A is subjected to the gravity of the horizontal and vertical downward, the pressure of C perpendicular to the contact surface of A, the support force of the ground to A and the static friction force F of the ground to the right horizontally of A, where the gravity g = 100N, the pressure of C to A n [A C] = 5 2, the support force of the ground to A is fn = 105N, A is balanced under the action of four forces, three of which have been obtained, and the friction force f of the ground facing the iron block A can be obtained by using the Cartesian coordinate method to decompose, and the magnitude of the friction force f of the ground facing the iron block A can be obtained, without making detailed calculations.

Give tips on how to do it, ask yourself to solve it, and turn it into your knowledge.

1. Make a force analysis diagram for C, (C is balanced by the force of the three common points), because the inclined plane is smooth, the support force of A to C is Na, and the perpendicular A inclined plane;

2. Make a force analysis diagram for A, A is balanced by four forces, A gravity, ground to A support force (upward), C to A pressure N'a, ground to A friction force (horizontal to the right).

It can be obtained by decomposing it in Cartesian coordinates.

3. The pressure of A on the ground = - (the support force of the ground on A).

Said for A. aSubject to gravity. Support, pressure. The frictional force and these four forces balance a and b each with a force of t1 = t2 = 10n. After force analysis, t1sin60=fa=5 2n.

2) T total = 100 + 100 + 10 = 210n, fn = t 2 = 105n

First, use the isolation method (1) 5 roots and 3 cattle.

Then use the whole method (2) 105 Ox.

Balance of Forces, Limit Thinking, Mathematical Method.

At the start (ob perpendicular to ab), fb=g, while fa=0;After moving A, the force is as shown in Figure 1, at this time FBG is obvious, then from Figure 1 to Figure 2, Fb is increasing, you can also use the limit idea, when pulling AOB to almost a straight line, Fb is infinite, which can also explain the process of increase. Taken together, FB decreases first and then increases. However, when the minimum value is not necessarily vertical, in our problem, except for G, everything else is changing, if the OA position remains the same (OA and the horizontal angle are unchanged), Fb is the minimum when vertical, as for when the minimum value is reached, we should use the cosine theorem in mathematics, it is recommended to use limit thinking.

Re-analyzing the fa, the beginning is 0, and then, looking at the plot, you can determine that the fa-has been increasing.

The idea of solving this problem is to draw a triangle at point p balanced by 3 forces.

One side (the tension of P to Point O) is fixed, and the other two sides change direction, and the pattern can be found by plotting.

The conclusion is: Fa has been increasing.

FB decreases first, reaches a minimum when Bo AO, and then starts to increase.

So you can only choose A

I don't understand hi me.

Three forces are balanced, and three forces can form a forward triangle, which is a problem of dynamic equilibrium analysis, and you can see it when you draw the diagram.

The force on the OA keeps getting bigger, and the force on the OB gets smaller first and then bigger.

I'm a physics teacher, and in this problem, the triangle of force, the balance of three forces, can be translated into a triangle, and the vertical force is gravity, and the left-side force is fa, and the right-side is fb

You'll see that I draw three** fa, which starts at 0 and gets bigger and bigger, and fb is originally g, and gradually gets smaller and bigger.

The answer to this question is A

b,d is definitely not right.

Initially, the fa is zero. Because in the horizontal direction the object is balanced. With the left shift of the A electric, the Fa gradually increases.

Assuming that the final state is that A o B is on the same level, then Fb is infinite, so option D is incorrect.

Brother is also just through the third year of high school, teach you some good methods, you can use it when you are unsure, Fa was 0 at the beginning, so it is impossible to reduce all the time, B is wrong, when A is infinite, the angle AOB is close to 180 degrees, it can be seen that at this time, FA, FB are infinite, so FB cannot be reduced all the time, D is wrong.

In fact, many multiple-choice questions can be tried with the elimination method when you don't know how to do it.

B is not true, there is no force at the beginning of FA (there is no force at the level) FB=MG

The FA FB horizontal component is the same after exercise.

Do vector triangles fa to become larger, fb first small and then large.

Choose A, the original force of Fa is 0, and then gradually increase, the original force of FB is equal to MG, when A moves, FB instantly becomes smaller, when AOB is greater than 90°, FB is equal to MG, and then it is larger and larger.

The parallelogram rule of force comes out easily.

The answer is A, how can your teacher say that the answer is D.

The tension of the front rope between the two objects f1=m1gsin30°

The tension of the rope touching the dust wall next to Yinqi is f2=(m1+m2)gsin30°

The combination of the whole parts, which is only used for stationary, has a concept of inertia and no frame of reference, ask the teacher, I can't explain clearly. M12 looks at the integrated analysis of the force, and the M2 is done. M1 is separated, the M1 force is analyzed, the M1 is done, and you can go to the banquet to do it.

This is a question of the remnants of the hail, the reason: the agitation does not give whether the board is smooth, or his friction factor, so there is no answer to this question!

I said: you can't just try to save trouble when copying questions! The conditions still have to be copied!