Physical problems of motion, mechanics

First of all, when you say frictionless, you should mean that there is no friction between the wooden block and the ground, and there is friction between the rod and the wooden block.

1) When stationary, the gravity of the rod is g=n*2=20 N.

2) set the friction coefficient j of the rod and the wooden block, the contact point with the ceiling is the fulcrum, for the sake of simplicity, the force arm of gravity is 1, then the force arm of elastic force n1 is 2, the force arm a of friction force is set, and the rod moment is balanced when pulling to the left.

Get 9*2+9ja=20*1

3) When pulling to the right, the moment balance gives n2*2=n2ja+20*1 and the above two formulas, and gives n2=90 8=Ox.

It's going to be drawn, but I can't draw it on my computer, sorry!

After the force analysis, it is enough to decompose.

It's a pity that you can't use pictures. It's troublesome to just say!

To put it bluntly, the frictional force of the two movements is in opposite directions.

A force analysis of the balancing force on the pair of rods will give you the results you said.

That's a tough question

Actually, I was about to ask, but I happened to see a benevolent brother answer this question, so I took the sheep and brought it over.

I don't understand it either

When pulled to the left or right, the friction force will also cause a certain moment, let the arm that supports the force be L1, and the arm of the friction force is L2

When pulled to the left, both the frictional and elastic forces on the rod produce a clockwise moment.

Total clockwise moment m1 = n1·l1 + f · l2 = n1 · l1 + a · n1 · l2 = n1 (l1 + a · l2) (note: a is the coefficient of friction).

Since the total counterclockwise moment is generated by gravity and is invariant, by being equal to the moment at rest, m1 = n · l1 = 10 · l1

So we get a·l2=l1 9

When moving to the right, the frictional force becomes a counterclockwise moment.

then 10·l1+n2·a·l2=n2·l1

Substituting can be obtained to obtain n2 = n].

Let's be this figure.

If someone can use a simpler method, try it, this moment has not been learned, can you use Newton's law force analysis to do it

Solution: Let the minimum initial velocity be v and the elevation angle be

According to the law of flat throwing motion, the equation of motion of the water flow is:

x=(vcos )t, and y vsin t-1 2gt 2 subtracts t, and v=-gx 2 2cos 2 *(y-xtan )=gx 2 [xsin2a-h(cos2a+1)]=gx 2 (x 2+y 2)[x (x 2+y 2)*sin2 -y (x 2+y 2)*cos2 ]-y

Let y x=tan , then x (x 2+y 2) cos , y (x 2+y 2) sin , the above equation becomes.

v 2=gx 2 (x 2+y 2)sin(2 - y, obviously when sin(2 - =1, i.e. 2 - =90°, therefore, the emission angle 45° 2 45° 1 2arctan(y x) = 45° 1 2arctan(4 3) = v is minimal.

and v g( ( x 2 + y 2) + y) = 3 10m s =

You're in college. The trajectory of the ants is an Archimedes spiral, so this problem is to use the Archimedes spiral, which is quite complicated to calculate, they meet at the midpoint of the equilateral triangle, so you can solve the distance between the three ants a, b, and c.

The number of distances a, b, and c traveled is actually to find the trajectory of the Archimedes spiral route taken by the ants.

The distance between each arm of the spiral is equal as.

2 a, according to r=a

The coordinate equation is:

r=10*(1+t)

x=r*cos(t*360)

y=r*sin(t*360)

The three ants do a constant motion of change direction, the trajectory should be a curve, and the arc gradually increases, because it is in a state of symmetry with the equilateral, and the place where they meet should be the center of the equilateral triangle, I understand that's all, I won't solve it, I hope it will help you a little.

Hello landlord, the ball has initial velocity when it is thrown upward, because the gravitational force g is vertically downward, so the gravitational acceleration is downward, so the ball begins to decelerate after being thrown upward, and it is impossible to accelerate again, when the velocity decreases to 0, the ball reaches the highest point, and then begins to fall, at this time it becomes an accelerated motion, because the direction of motion and the direction of gravitational acceleration are the same.

This should only be a physics question at the level of the second and third years of junior high school, and the teacher should not make such a low-level mistake.

According to the test requirements of junior high school, the resistance of such questions is generally negligible, and the movement of the ball can be regarded as a uniform speed to be calculated without considering the resistance, and when the resistance needs to be calculated specifically in high school, the movement of the ball is actually a movement with variable speed.

Friend, can the rocket be the same as the ball The ball has no upward force except for the force of the initial velocity given to him by the hand, and it cannot produce upward force by itself, and the rocket itself has an upward propulsion force, otherwise how can it be lifted off The rocket is in the process of rising, the downward gravity and drag are there, but the upward strong propulsion force it has is greater than everything, and the resultant force is upward.

The teacher should have said that the speed of the shot is v, so during the time when you reach the highest point, you do a deceleration movement, and your understanding is correct.

When you don't throw it, the speed of the ball is not 0, and after you throw it, there is a speed amount, which is a very short period of time There is an element of acceleration. Think about it, isn't it.

The landlord's idea was correct, but the teacher did not explain it.

The arm gives the ball an acceleration, and the moment it leaves the hand to the highest point, the process is deceleration.

It seems that your teacher is a parallel import, and you must not delay your future because of a parallel teacher.

The teacher is wrong, after the ball is shot, it relies on inertia to rise, the kinetic energy decreases, the gravitational potential energy increases, the speed slows down, after reaching the highest point, the velocity is zero, and then the ball falls, and in the process of falling, the gravitational potential energy decreases, the kinetic energy increases, the speed becomes faster, and the moment it comes into contact with the ground, the speed is the fastest.

From the meaning of the title, we know that f=, f=, so t=, so a1=1m s 2f=so a2=2m s 2

Therefore, it is concluded that t=1s, so the constant force pulls 2t=2s

Therefore w=f*t=

vmax=a1t=2m/s^2

e=<>

1) Constant force work = total work of friction =

2) Kinetic energy maximum = velocity maximum.

Suppose the displacement when the constant force is withdrawn is s

s = 2 meters. Only the work done when the frictional force is evenly decelerated is the maximum kinetic energy (3-2).

Knowing from the a--v plot line:

When v=0, a1=4m s2, the wind is zero.

Therefore: mgsin37°- mgcos37°=ma1 is easy to find = by substituting data

When v=5m s, a=0

So: mgsin37°- mgcos37°+kvsin37°)-kvcos37°=0

Substituting the data yields k = 16 19

μ=k=38/40

Boy, the question of Shanghai in 07, think about the process yourself.

Let the spacecraft be x from the center of the earth at time t

Then there is: a=-gm x

The two ends of the above equation are integral to x, and we get.

adx=gm/x+c

again a=dv dt

1/2*v²=gm/x+c

Again, when t=0, v= (2gr).

1/2*v²=gm/x

i.e. v= (2gm x).

Get (x)*dx=(2gm)dt

Integral: x (3 2)=3 2[( 2gm)t+2 3r (3 2)]

again g=gm r

Namely. x^(3/2)=3/2

Then substitute x=nr to get the answer.

The height from the ground is different, the g value is different", it is not a simple linear motion with uniform speed. To calculus.

There are two effects of force:

Force can change the state of motion of an object;

Force can deform an object (or force can change the shape of an object).

1) Force can change the state of motion of an object.

Understanding] Whether the motion state of the object changes generally refers to: whether the speed of the object changes (the change in the speed of motion) and whether the direction of motion of the object changes;

The motion and rest of an object are relative, and rest is a special state of motion. Whether the object is moving from rest to motion, or from motion to rest, or there is a change in the speed or direction of motion, it can be considered that the motion state of the object has changed.

Experiments illustrating that "force can change the state of motion of an object" and examples are listed:

Example] A small steel ball at rest is attracted by a magnet and moves in the direction of the magnet;

The small steel ball that does linear motion on the smooth horizontal plane is attracted by the magnet placed in the position of the direction of movement, and the speed becomes faster;

The small steel ball on the smooth horizontal plane is attracted by the magnet placed in a position perpendicular to the direction of movement, and the direction of movement changes, and it moves in the direction of the magnet;

The baseball player throws the ball with great force, and the ball changes from stationary to motion;

The soccer goalkeeper catches the soccer ball that shoots into the goal, and the soccer ball changes from motion to stationary;

2) Force can deform an object (or force can change the shape of an object).

Understanding] To observe the deformation of an object, it must be observed when the force is acting, because some objects are deformed, and after the force is withdrawn, the deformation is restored, while some deformation cannot be recovered;

Experiments and examples illustrating that "force can deform an object (or force can change the shape of an object)".

Example] Under the action of tensile force, the length of the spring is elongated;

Under the action of pressure, the length of the spring is shortened;

Pull a rubber band with both hands, and find that the rubber band becomes longer under the action of force;

Knead the plasticine by hand, and the plasticine will turn into various shapes;

Under the force of the archer, the bow is pulled apart and the shape of the bow changes;

The moment the foot hits the ball, the shape of the ball changes;

I hope it helps you, and if you have any questions, you can ask them

I wish you progress in your studies and go to the next level! (*

1: Change the motion state of the object.

2: It is the deformation of the object.

It is what happens to the object after the force acts on the object, for example, if you hit the table tennis ball with a racket, the ball will fly away, which is to change the state of motion, and the shot put falls into the sand, and the sand depression is deformation.

The first is to change the state of motion of the object, and the second is to deform the object, and to understand it, to change the state of motion of the object, and the change in the direction and velocity of the motion is considered to change the state of motion, as if I kicked the ball hard and the ball flew away, which is to change the state of motion, and to deform the object, as if I had flattened plasticine with one foot.

Examples of changing the state of motion of an object: kicking a stationary ball away, pushing a toy car away, lifting a heavy object, rowing and running (interaction forces).

Examples of deforming objects Breaking glass, stepping on plasticine, flattening boxes, compressing springs, and bending iron plates.