Science and physics competition questions in the second year of junior high school, science competit

When the gravity of the weight B gradually changes to the ox, the object M is about to start moving (actually not moving), and the friction force at this time is right, and it can be explained that the maximum friction force between M and the table is the ox.

Then slowly fill water into the container C, when the volume of the weight B has 1 4 exposed to the water surface, the object M will start to move again, and the friction force between M and the table is also the maximum friction force at this time, that is, the cow to the left, and it can be known that the pulling force of B to M at this time is the ox.

According to the analysis of the force of B, after injecting water into C, B is subjected to gravity, buoyancy and tensile force, and the gravitational ox and tensile ox are known, and the buoyancy force is known as oxen.

Buoyancy = density of liquid * volume of water discharged by the object * g

Now let the density of b be x, and we can know x*vb=, and we can know vb=.

By substitution, it can be seen that buoyancy = density of liquid * volume of water discharged by the object * gx = kilogram m 3

When m is about to move for the first time, the friction of the table against m is in the right direction and is the maximum static friction.

When m is about to move for the second time, the friction of the table against m is in the direction of the left, which is also the maximum static friction.

Float. F float = p water g * 3v 4

v=4 3 dm 3 can be found

So pb = 1125kg m3

It's been a long, long time since I left middle school.

This question shouldn't be too difficult, but I really can't at the moment, waiting for the master to answer.

c, the evaporation of water in the two cups is the same;

Most of the water absorbed by plants is transferred to the air through transpiration, and only a small part is photosynthesized, and photosynthesis causes a non-significant decline in the left end.

1.The masses are equal, the solid spheres a, b, m A = p A v A, m B = p B v B, M A = m B, so P A v A = p B v B, so substituting the above equation 2 * v A = 4 * v B, so va:vb = 4:

2=2：1.It should be that your answer is wrong.

2.The buoyancy ratio of the two balls is 6:5, so the ratio of the volume of water discharged is 6:

5, because they have equal mass, if both of them float on the water then their buoyancy is the same, now 6:5 indicates that A floats on the water surface B sinks to the bottom, and the water va is discharged by MA=P Vbpb, and the volume ratio of the two spheres is 2:1=10:

5 so know v row 6va 10 = 3va 5, substitution.

pb=pwater3*2 5=, so pa=

In Archimedes' theorem, m = the volume of boiling water for the object. And because the mass is the same, the density is different, according to m=pv, the volume ratio of the two is calculated. Then substitute the proportional calculation.

equal mass, solid ball, density ratio 2:4, volume ratio 4; 2.