Urgent physics topics, physics topics urgent

1. F= mg, then =20 100= unchanged 60nn. Because the object is not pulled during the whole process, the force is flat at any time.

Balanced. That is, when the tensile force increases to 25N, the static friction force is also 25N. The resultant force is 03, (this question seems to be a bit problematic: "The average velocity at the end of the third second is 9 meters and seconds" is.)

Wrong to say, either the instantaneous velocity at the end of the third second, or the average velocity within the third second.

Degree. If it is an instantaneous velocity, then the velocity is reduced by 1m s in 1 s, and the acceleration is -1 meter each.

square seconds; If it is the average velocity, then the instantaneous velocity at the end of the third second should be 8m s, then.

The acceleration is -2 meters per square second.

4. At the moment of hitting, f=ma, and g=mg=2n, f=10n, so when a=fg, a is.

50 meters per square second; Since the machine is only instantaneous, the horizontal plane is smooth again, and then the horizontal square.

If there is no force to act on it upwards, then the acceleration will be 0

5. PV=NRT will not be done for a long time, please be smart.

60n2:25n 0n

3:-1m/s2 42m

Avogadro's formula PV=NRT, note the conversion of the thermodynamic temperature scale to the camera temperature scale).

Well, I haven't studied a lot.

1： ,60n。

2： 25n，0n。

3: 1 meter in a quadratic second, 42 meters (The trap of this question is that the train is doing uniform linear motion in the first 1s).

4： 50（g=10m/s2），0。

5: , calculated by c=pv t, c is constant, p is pressure, v is volume, t is kelvin temperature. The standard condition is 0 degrees Celsius, 1 standard atmosphere).

Slide at a constant rate, indicating mgsin = umgcos

1) If the velocity rises uniformly, then F-Mgsin = UMGCOS to obtain F=2mgsin

2)u=tanθ

Let the bullet penetrate the steel plate at a velocity of V1, the velocity after penetrating the steel plate of 2d is V, the drag force is F, and the depth of the bullet into the second steel plate H

Then mv1=(m+2m)v

2df = 1 2mv1 square-1 2(m+2m)vsquare.

The expression f can be obtained.

Let the velocity of the bullet be v2 when the first plate is fired, and the velocity of the bullet when the plate is v3 and the velocity of the bullet when it stops at the second plate is v4

mv1=mv2+mv3

1 2mv1 square = 1 2mv2 square + 1 2mv3 square + fd to obtain v2 = (3 + root number 3) 6v1

mv2=(m+m)v4

FH = 1 2mv2 square - 1 2 (m+m)v4 square square.

Find s=d(2 + root number 3) 4

over

Open circuit Short circuit Open circuit Total power supply (it should mean unplugging the microwave oven).

In summer, the weather is very hot, Xiaoliang's house is on the vertical air conditioner, Xiaoliang is watching TV, and his mother is cooking in the kitchen. The moment she turned on the microwave, the air switch in the circuit "tripped". The cause of the trip may be a short circuit inside the microwave oven plug or it may be too much power from the electrical appliances in the circuit

If you want to use electrical appliances to work normally, one is to check whether the microwave oven plug is short-circuited If so, the fault should be eliminated;

The second is to turn off the microwave oven and then turn off the air switch.

Open circuit short circuit Open circuit Microwave oven.

1. Inaccurate Add the propagation time of the sound, 100 340=

So the athlete performance is.

2. The shape of the small hole does not affect the imaging.

1.Not accurate, there is time for sound to travel.

t=2.No change.

1.Incorrect, the sound takes t=s v=100m 340m s= from the start to the end, so the actual result should be seconds.

2.The image of different shapes of holes is the same, that is, the image of holes is not affected by the shape of the holes.

The first way: t=s v=100m 340m s=

The second way: do not change the shape of the image.

1) When the conveyor belt runs at a constant speed of v=2m s, the object is accelerated first and then at a constant speed because of l v*t.

The average velocity of the acceleration phase is (0 v) 2 v 2, so l s accelerates s at a constant speed (v 2)*t plus v*(t t plus).

That is, 10 (2 2)*t plus 2*(6 t plus), the acceleration time is t plus 2 seconds.

2) If the conveyor belt running rate is increased, in order to allow the object to be transported from A to B in the shortest time, the object must be uniformly accelerated throughout the whole process, and the speed when it reaches B is set to Vb, then the conveyor belt should run at least Vb.

First, use the first case to find the acceleration a of the object, add by v a*t, get 2 a*2, and get a=1 m s 2

The whole process is accelerated to B, and VB 2 2*A*L is used to obtain VB 2 2*1*10, and VB 2*root number is 5 m s

That is, the operating rate of the conveyor belt should be at least 2 * root number 5 m s

3) If the running rate of the conveyor belt is doubled on the basis of the basis again, then the object still moves according to the original acceleration, and the time obtained is still obtained by the total of vb a*t, 2 * root number 5 1 * t total, and the time obtained is t total 2 * root number 5 seconds.

The text version is not easy to type, look at the picture.