High One Physics, Kinetic Energy Theorem, Emergency 5

f is not a constant force, one is to use calculus, and the other is to use the kinetic energy theorem.

Regarding the kinetic energy theorem, first find 2 states, generally the initial state and the final state.

Here the two forces do the work, the frictional force and f, the kinetic energy of the initial and final state changes to 0, that is, the work of the two forces is equal.

Pay attention to the time of action of the analytical force.

fAction10sFriction for 15 seconds (note, to find the displacement) to find the displacement of the work.

It seems that on the V-T diagram is the area (I forgot the specifics, if it doesn't work, I will be stupid to solve it) Regarding the maximum instantaneous power, I didn't encounter it when I was in school, so the problem is fine.

A typical kinetic energy theorem.

Gravity work (negative work) Positive work of pulling force (s2 does not do work).

Just pay attention to the displacement.

The process will not be given to you (lazy).

It's a test of your understanding of the theorem.

Physics requires a strong understanding of theorems.

Otherwise, it is useless to do no matter how many questions you do.

Formula: ek = w = 1 2mv2 squared - 1 2mv1 squared.

10 fs f=ma=f=1n

s=s=10m

w=10j2)p=wt=1w(f).

3) The power is maximum when f=f. p=fv=1w...Wait.

2）p=w\t=

Question 2. v = root number 2as = 10m s

On the punch 5MH=3M

ep=mgh=150j

E end = ....100j

v end = ....Root number 40m s

It's purely verbal and irresponsible.

But the solution is correct.

If you learn from the physics teacher, he never counts, only the solution: -d

Let the motion y meters after the tensile force is removed, and by the kinetic energy theorem, we get: 0 0 10xcos37x10

y), solution y 6

The slider is subjected to gravity, support, and friction on the inclined plane.

Analyticable: gravity does negative work, support force does not do work, friction force does negative work (here the dynamic friction factor is first represented by k) - mgh-kmg*cos = 0-1 2mv (2) here the square is hl = h sin

According to the decomposition of the force, it can be known that the pressure of the object on the inclined plane is f pressure = f * cos 30 degrees = root number 3 2mg

The friction force f = pressure = root number 3 10mg

direction downward) according to VT2

v022as

vt=0s=v02 2a=16 2 (root number 3 10g + 1 2g) is substituted into g =

Get s=

Since the kinetic energy of the object at rest is 0, the mechanical energy of the front and rear systems (object + slope) remains unchanged.

mgh + f*2h=, where f = cos30*mg, substituted to get h = i.e. 8 (1 + root number 3).

Therefore s = 2h = i.e. 8 (1 + root number 3).

Solution: (1) The mechanical energy lost by the student during the impact with the ground is: e=mg(h-h) The solution yields e=330j

2) Let the time taken for students to fall from a height of h to the floor be t1, and the speed when they first touch the floor is v1; **The velocity at ground is v2 and the ascent time is t2, which is determined by the kinetic energy theorem and kinematic formula.

Falling process: mgh = mv 2 2

Solution: v=6m s t=

Ascending process: mgh = mv2 2

Solution: v=5m s t=

The student's contact time with the ground is t=6-5=1s

Let the average impact force of the ground on the student be f, and the upward is positive, which is determined by the momentum theorem (f-mg)t= m(v1+v2).

Solution: f=1260n

According to Newton's third law, the average impact force of the student on the ground f=1260n is downward in the direction.

The difference between the potential energies at the maximum height of the two is used to give an idea of the lost mechanical energy.

Knowing the height of ** can find the velocity of **, and the amount of change in kinetic energy is equal to the impulse (momentum theorem) during this time

You're on the right track.

Let the angle between the line connecting the point at the time of departure and the center of the sphere and the horizontal angle be . h=rsinθmgsinθ

mg(r-rsinθ)+

Lianli finishing: 3sin

Solve this trigonometric equation and solve it yourself. (You verify the equation with sin = ).

First of all, there is no problem at all, the inertia force is magnitude, and the direction is horizontal to the left. When the object leaves the sphere, the pressure of the object on the sphere is exactly 0, and the centripetal force is the sum of the inertial force and the gravitational force in the radius direction. The kinetic energy theorem because you chose the sphere at rest, i.e., the sphere as the frame of reference.

In the kinetic energy theorem, the force doing work should be the inertial force and the gravitational force, is it not written that the inertial force does the work!

m 3 kg, h 2 m mill bush, h m.

1) Let the average resistance of the shot put ball in the sand be obtained by applying the kinetic energy theorem in the whole process.

mg*（h＋h）－f *h＝0

Get f mg*(h h) h 3*10*(type 2 yinvern cattle, the direction of resistance is vertical upward.

2) Let the shot put (your title is inconsistent with the same word, I call it "shot put") when it first falls to the surface of the bunker is ek

From the phase of air movement, mechanical energy is conserved.

ek mgh 3*10*2 60 joules.

3) The work done by the shot put to overcome the resistance of the sand is w gram resistance f * h 330 * joules.

Kinetic energy theorem copy w = ek w refers to the total work.

There are two ways to find the total work: 1 first find the combined external force, and then find the work, 2. first find the work done by each person, and then find the algebraic sum.

As for the good method, it depends on the specific situation: for example, the resultant force can be found through force analysis, or the displacement of each force is the same, that is, the external force can be found first, and then the work can be found. If the displacement of each force is different, then it is better to find the work done by each person first, and then find the algebraic sum.

As for the occurrence of variable force: 1 is that when the surface is moving, friction does work, and the kinetic energy theorem is often used directly to find friction to do work.

2.When the car starts, for the car to start at a constant power, the traction force (variable force) is used to find w=pt.

To sum up, you still have to do more questions, summarize more, and think more!

The Kinetic Energy Theorem and later you will learn du

The theorem of conservation of mechanical energy is the core of high school physics, and the lower inner few are the basic routines when doing the problem.

1) Clarify the object of study, generally referring to a single object.

2) Perform force analysis on the research object.

3) Find out the work done by each joint force or the grandfather.

4) Clarify the beginning and end states, and determine their kinetic energy.

5) List the equations according to the kinetic energy theorem.

6) Solve and check.

If you learn to combine the use of the law of conservation of energy and the theorem of kinetic energy.

The conservation of energy can solve the problem of work done by variable force. To do physics problems, you need to analyze the physics situation, such as which forces do the work, which forces do not do the work, the physical state before and after the work, etc., and you have to be patient and careful, and you would rather do less than make more mistakes. Hope it can help you and good luck!

In high school, the work done by variable force is not examined, but mainly asks about the work done by variable force, so it can be solved according to the functional theorem, for example, the amount of change in kinetic energy can be equal to the work done by the resultant force, then it means that you have found the total work, and you can find the work done by variable force by subtracting the work done by other constant forces.

It relates work and kinetic energy, without considering acceleration. It is easy to solve the problem, and the work done when encountering variable force depends on whether it is a linear change or a nonlinear change.

Let the friction force be f, then it can be obtained by =2as.

v²=2s（mg+f）/m

7v/8）²=2s（mg-f）/m

1) Syndicate the formula, which can be solved to obtain f=15mg 113(2) to bring f into v =2s(mg+f) m, and the solution is s=113v 256g

3) Conservation with energy, mv 2 = fs

Desirable s