200 for the second year of junior high school physics, and 200 for the second year of junior high sc

1) The first statement is correct, an object can do work, and the premise is that it must have energy (which can be understood by analogy as ability).

Because the process of doing work is the process of converting one type of energy into another, and the fact that an object can do work means that it has energy that can be converted into other energy.

The second sentence is wrong, the object has done a lot of work, it can only mean that there is a lot of energy transformed, but how much energy is left can not be determined, just like a good kind person in the society to raise donations, the one who donations more may not be the most money, ha.

If you change it to an object, the more work you can do, then it is correct.

2) Hourly flow m= water v=1 103kg m3 400m3 60=w=mgh=

p=w/t=

1) Because the wood floats on the water, the two forces of gravity and buoyancy are balanced, so f float = g wood (2) If you want to learn physics well, you must remember various formulas, master various concepts and definitions, and be able to apply them. Remember.

The first question belongs to the second year of junior high physics: all correct. As much work as an object does, it has as much energy as it has!

The second question belongs to the third year of junior high school: 400m min water = drop h=70m, if you do not calculate the efficiency loss, power =

The mass is about: 8 10 3 60 10 -3 = 480kg

Then to "carve" a 35kg statue, the volume of material required is about 35 8 = cubic decimeters.

Looking at this density of 8 10 3kg m 3, it has already surpassed steel, and it is estimated that it is a ferroalloy, most of which is cast, not carved.

Xiao Ming is 3:2 than Xiao Gang

Let the length of the wooden stick l, the distance between Xiao Ming and O point L1, and the distance between Xiao Gang and O point L2, with the shoulder of Xiao Gang as the fulcrum: F1L=GL2

Take Xiaogang's shoulder as the fulcrum: F2L=GL1

Solving the system of equations yields l1:l2=3:2

Solution: Let the distance between Xiao Gang's shoulder and point O be L1 and the distance between Xiao Ming's shoulder and Point O is L2, then according to the condition of lever equilibrium, it can be known that (3g 5)l1=(2g 5)l2

Then: L2 (3G 5).

l1 (2g/5)

1) Xiao Ming can move the hanging point to himself or close to the hanging point.

1.The work done by thrust on the cargo w total = fs = 100n 10m = 1000j useful work w has = gh = 100n 6m = 600j extra work w = w total - w has = 1000j-600j = 400j because w = fs (the reason for the extra work on the inclined plane is because of friction), so, the friction f = w amount s = 400j 10m = 40n2There are many types of machinery, such as fixed pulleys to change the direction of force, and laborious levers to save distance (in fact, labor).

3.There are two ways to connect the two pulleys at a time, if the final three sections of the rope pull the moving pulley, that is: the direction of the pulling force is upward, then at this time, only the effort can be saved, because the direction must be vertical upward, can not be changed.

4.An approach bridge, as the name suggests, is a section of road that directs vehicles onto a bridge. There are many rivers that need to be navigated, so the bridges built on them need to be of sufficient height.

The slope of the approach bridge should not be too large, so the higher the bridge, the longer the approach bridge will be, so that vehicles can easily climb onto the bridge. The main use of the inclined plane here is also good for the life of the bridge.

Slowness is not taking into account the kinetic energy of the object.

So w total = 10 * 100 = 1000j

The potential energy of the goods increases w = 10 * 10 * 6 = 600w Mo = 1000-600 = 400J.

So overcome friction and do work 400 joules.

1 can be labor-saving or distance-saving, or it can only change the direction of the force.

2. The fixed pulley changes the direction, and the movable pulley changes the size of the force, and the movable pulley must be used to save effort.

3. The function of the slender approach bridge is to reduce the slope of the car on the bridge, and it is easy for the car to get on the bridge.

The work done by thrust on the cargo is: w total = fl = 100nx10m = 1000jw has = gh = mgh = 600j

The work done to overcome friction is: w amount = w total - w has = 400j"The purpose of using machinery is to save effort"Not exactly. For example, cranes, fishing rods, etc., do not save effort, but to save distance;

Using a fixed pulley and a fixed pulley to form a pulley group, can achieve the two purposes of labor-saving and changing the direction of force at the same time" not all pairs, such as when the n of the composed pulley group is 3, the pulling force is upward, and the force can be saved, but the direction of the force cannot be changed.

The slender approach bridge can prevent the damage caused by inertia"No, the use of inclined planes can save effort.

1 From the question, it can be seen that the thrust does the total work, and the thrust is 100N, and it moves 10m on the inclined plane, so the total work of w = FS=100N x 10m = 1000J The work done to overcome friction is extra work, w extra = w total work - w useful w useful is the work done by the object = gh, g object = mg = 10kg x 10n kg = 100n , so w useful = gh = 100n x 6m = 600j so w extra = w total work - w useful = 1000j - 600j =400j

w=f*l=100*10=1000(j)

Q = W-W useful = W-MGH = 1000-10 * 10 * 6 = 400 (J) The purpose of using machinery is to save effort (change the direction of force) to use a fixed pulley and a fixed pulley to form a pulley group, which can achieve the two purposes of labor-saving and changing the direction of force at the same time (the fixed pulley can only change the direction of force).

A slender approach bridge can prevent the hazards caused by inertia (the actual situation should be considered, and the safety of the long bridge itself should also be considered).

The thrust is 100N, which makes it move upwards by 10m W fl, and the W push is 1000J....How do you horse friction factor not have the forehead.

(1) W=FS=100N*10M=1000J (2) The use of machinery can save distance (3) The use of fixed pulleys to change the direction of the force can not change the magnitude of the force.

There may be a misunderstanding here.

Normally, if we specify that the pressure of all four feet is this value, then we assume that the pressure is this n.

For example, if we use two sections of rope to pull an object of 10N, and the pulling force of the rope is 5N, we naturally think that the pulling force is 5N, regardless of the sum of the pulling forces of the two ropes.

If you want to find the mass of the bison, then you have to multiply it by 4.

Instead of multiplying 4, the four feet of the buffalo are independent of each other, and the pressure on the ground is 2x10 5pa. This pressure cannot be stacked. You can think of the buffalo as a one-legged monster, and the base area of one foot is equal to the sum of the areas of the four feet.

this topic.

You count the square meters of the area.

If you multiply by 4, that's square meters.

Is there such a large area on the soles of a cow's feet?

So according to common sense: no need to multiply by 4.

itself is a paraffin model of four footprints.