From the first to the second year of junior high school physics questions, can you help?

1. All solids, if their velocity does not change, must not be affected by the action of resistance, his opinion is wrong! If the velocity does not change, then he is not subjected to force or the net force is zero. For example, if you pull a wooden block by hand to do a uniform linear motion on a rough plane, the wooden block is subject to both resistance and tensile force, and the two forces are equal in magnitude and opposite in direction.

Another example is that when a car moves in a straight line at a uniform speed on the highway, it is subject to resistance.

Second, if you let the car slide down from different heights, please reason that the car moves on a plane with 0 resistance at different speeds, and his final speed will not be the same. The initial velocity is different, and it is not affected by external forces, and will keep the state of motion unchanged. At this time, I understand:

The movement of the trolley on a plane with a drag force of 0 is not subject to drag and is not affected by other drag effects such as air resistance, other external forces other than gravity and support forces

Hello: 1) Not true. Think of a car driving on the road at a constant speed, with the same speed, but with resistance.

2) Different. In uniform linear motion, "constant velocity" refers to the starting velocity, so the same height should be determined. Different heights, different speeds. Hope.

No, it will always maintain a uniform linear motion, and it will not receive a balance and its speed will not change.

The speed does not change, which can only indicate that the object is moving at a uniform speed, and the prerequisite for uniform linear motion is that it is not affected by external forces or is acted on by equilibrium forces. Needless to say, the constant speed curve motion is bound to be acted upon by an external force.

2.(1) What is the design of the ballpoint pen to reduce the friction of the good school?

The balls of the ballpoint pen are in a rolling state during writing, which belongs to changing the sliding friction to rolling friction, reducing the friction and writing more smoothly (borrowed from the previous one).

2) What is the design of the ballpoint pen to increase friction?

The pattern on the barrel of the ballpoint pen increases the roughness of the contact surface, increases the friction, and makes the grip of the pen more envious.

The previous one's really good friend code.,I quoted it.,Mine should be added.。 ）

1. Ancient Egypt's rolling wood and boulders used to change the sliding friction to rolling friction, so as to reduce the friction of handling, 2. After the road surface splashed water and ice on the land, the ice surface was formed, and the ice was smoother than the ordinary roadside, which was used to reduce the roughness of the contact surface and reduce the friction.

3. The beads of the bead early chain hall pen are in a rolling state in writing, which belongs to changing sliding friction to rolling friction to reduce friction and write more smoothly.

Gravity of the tractor:

g = mg = 5000kg * 10n kg = 50000n tractor pressure on the ice:

f=g=50000n

The contact area between each track of the tractor and the ground:

s=25m*28*10^-2m=7m^2

The pressure of the tractor on the ice:

p1 = f1 2s = 50000n 2 * 7m 2 = because there is: p1 = so this tractor can pass through the ice.

The maximum pressure that the ice can withstand:

p2=p-p1=

The maximum weight of the object can be loaded:

f=ps=9440pa*7m^2=66080n

The mass of the tractor is 5000kg, the gravity is g = mg = 5000 *, the contact area between the two tracks and the ground is s =, so the pressure is p = g s = 49000, 98000-35000 = 63000pa, so it can withstand the external weight of f = 63000 *, so the mass that can be loaded is m = f g = 88200, and the maximum weight of the object can be 9000kg

According to p=f s, the maximum gravity f= of the river surface can be obtained to the power of 5 cattle, and according to f=mg, m=

Answer: Can pass up to m object = m-m drag =

Why isn't it the topic of the first year of junior high school?,Speechless、、、 handed over to other prawns、

Suppose that the mass of aluminum required for this steel part is x kilograms, then the early shortage volume is x (if it is made of steel, the mass of steel is (x+104) kilograms, and the volume is (x+104) (

Because they are the same kind of parts, they have the same volume.

So there is x (

The resulting x = 54

So when made of aluminum, 54 kg of aluminium is used.

Specific heat capacity x mass x temperature change = heat absorption.

c * 60 * (which shirt 35-15) = 5040000c = Li Na cavity.

It is eggplant-type water.