Ask for help for physics questions in high school, ask for help for physics questions in high school

Imagine that this problem should be a wooden stick placed horizontally to the left and right, so when the constant force of f is received in section b, for the whole there is, t=ma

For wooden sticks, there should be a equal everywhere, so take a microelement with a mass of m = m x l at a distance of x, and have t = ma.

The tension received by this microelement is the tension on the right side minus the tension on the left side (a to the right, then the right t is greater than the left t. Therefore t right x - t left x = t=ma x l. Therefore, t right x = t + t left x, which is a uniform increase, is a linear function with respect to x, so d is chosen.

You can also continue to calculate, at point a, it is easy to know that t left a = 0, there is t right a = t. Then there is t, t right x = t = ma l x = max l, choose d

If the mass of the AB bar is m, then the tension t= m'a m'= m l x , a=f m at the coordinates x on the bar

Bringing the above two equations into the * equation yields t= f l x, i.e., a primary function where t is x.

I hope you can, if you don't understand, you can ask me again. Thank you.

Good luck with your studies, hehe.

cBecause it is a constant force, impure is changing.

Select a problem of gravitational moment.

Draw an image of f-t, the area enclosed by the plot line represents the impulse of the force, and then solve it according to the kinetic absolute quantity theorem (the impulse of the resultant force on the object and the bond of the body is equal to the change in the momentum of the object!). ）

The problem of variable force is dusty, and points are used:

f(t) brother laugh = 2t + 2

m=2a(t)=f(t)/m=t+1

v(t)=v0+ (0,t)a(t)dt (0,t)(t+1)dt

t²/2+t]（0，t）

t²/2+t

v（2）=2²/2+2=4

Solution: (1) Because the velocity decreases to zero, a=v t=80

2) From the formula v at the end of 2-v at the beginning of 2=2as, 80 2-0=2 32 s is obtained, s=100m

3) The resultant force f does negative work on the aircraft, so that its speed decreases, f = am = 20000 32 =

LZ: This shouldn't be some 38-minute homework series of holiday assignments......

1. From p=fv and f-f=ma (f is the resistance), a=(p m)(1 v)-(f m); The slope k, k=a(1 v)=(f m) (1 v)=fv m=p m, the value of constant power p can be obtained by finding the slope k, k=a(1 v)=fv m=p m, so the a option is excluded.

When 1 v=0 is obtained from the plot, a=-2m s 2, so -2=-f m, the value of the resistance can be obtained, and the c option excludes.

Because when the velocity is maximum, that is, when a=0, at this time, f-f=0, p=fvmax=fvmax, you can find the maximum velocity vmax, and the b option is excluded.

The D option is wrong in the whole acceleration process is variable acceleration, and there is no way to find the time to reach the maximum velocity using a known formula in the variable acceleration process.

2. When the child pulls the boat in case A, only his own boat is displaced in the direction of force, and in case B, there is also the empty ship that is displaced in the direction of tension, that is, the total displacement caused by the second condition is greater, and the magnitude of the force is the same, so the work is more done (extra work is done on the empty ship), so w1 w2, and the power p=w t and t is equal, get p1 p2Therefore, C. is chosen

3. According to the figure, the orbital radius of the spacecraft is r=r sin( 2) (no problem solving right triangles, right?) ), according to v=2 r t, option a is correct;

The period of the spacecraft is t, and the time of day is t0, because such a "total solar eclipse" occurs once in a cycle, so the number of times the spacecraft experiences a "total solar eclipse" in a day is t0 t, and option b is wrong; (Be careful not to take into account the revolution of the Earth, as the period of the Earth's revolution is much larger than that of a spaceship).

According to the figure, it can be seen that the central angle of the arc passed by the total solar eclipse is , so the time of the total solar eclipse is t 2, and the c option is wrong;

According to gmm r 2 = m(2 t) 2r (gravitational force provides centripetal force), the d term is correct.

There are still unclear questions to ask.

1) According to the title, got.

by f-f=ma

p=fv has f=p v

p/v-f=ma

From the known graph, the corresponding points v1 and v2 of the two velocities and the corresponding points a1 and a2 of the two times can be obtained

then there is a system of equations.

p/v1-f=ma1

p/v2-f=ma2

The values of p and f can be solved.

So AC is right. by p=fmaxvmax

vmax can be obtained from vmax

Therefore B is right. There is a set of vmax=v0+at

t=(vmax-v0)/a

But neither v0 nor a knows.

Therefore, it is impossible to find t, d is wrong.

How did you get it, it looks good.

Let the desired time interval be t, then t t* (n 1).

obtained from h g*(2t) 2 2.

The acceleration due to gravity is g h (2*t 2) h h*(n 1) 2 (2*t 2).

Solution: The motion of water droplets can be approximated as free-fall motion. When the nth drop falls on the plate, the n+1, n+2 drops, their interval time is the same as t=t 2, and each small drip cycle t is the droplet free fall time, so t=t n

H=1 2gt yields:

g=2n²h/t²

The n+1 drop is now falling displacement:

hn+1=1/2g（t/2）²=1/4h

It is also at a distance from the height of the disk: h=h-hn+1=3 4h, so the acceleration due to gravity g= (n+1) 2t h according to the formula h=1 2g t

For the children's shoes on the 1st and 2nd floors, if the nth drip falls into the plate, what does n-1 represent? It should be n+1 n+1 is the drop that is falling in the air, and n+2 is the drop that is about to fall from the faucet.

The time is measured from the first drop to the n-th drop, and since there is no time interval for the first drop, the drip time interval of n-1 is shared. If the time t is shared, the time interval between the faucet dripping is t (n-1).

So, g=2h [2t (n-1)] 2 h*(n 1) 2 (2*t 2).

Do a force analysis, after lifting the object, the two sections of spring are 90 degrees, and the force they give to the object is equal, and the direction is 45 degrees along the spring direction and the vertical direction. Then their net force is equal to the gravitational force of the object, and the direction is opposite. It can be seen that the magnitude of the force component on each section of spring is ( 2 2) g { Supplement:

The root number of the second half is multiplied by g}, then from the spring Huke's law f=kx, where x is the change in the length of the spring, it can be seen that the elongation of each section of the spring is x=(2 2k)g, the total elongation is (2 k)g, and the final total length is l+(2k)g, and the spring elasticity is (2 2)g.

Hope it helps.

1 is balanced by two forces: the net force of the spring = the gravitational force of the object i.e. f=g which is 2 times the root number, so f=g the root number 2

2 By f=kx so x=f k, the total length of the spring = l+2x

To do this kind of problem, you need to draw a force analysis diagram.

f = g 2 times the root number

From f=kx, x=fk=g k is 2 times the root number, so the spring is now x+l

f=g root number 2

Length = root number 2 g k l

How do you hit the root number??