Physics questions! Velocity! Thank you, big brother, big sister!

If we ignore air resistance, the bomb will fly at the same speed as the airplane after it is dropped. That is, the bomb is in a uniform linear motion in the horizontal direction, and in the vertical direction it is in free fall. It is also known that the bomb is directly below the aircraft at **.

Then the time required for the bomb to hit the ground is t = 2h g = 20 seconds under the root number. After that, the plane flew for another 10 seconds before the sound was heard. Draw a simple triangular model to find out.

2000 squared + (10v) squared = (330x10) squared. Pythagorean theorem. The speed at which v can be solved.

Because the air resistance of the bomb is negligible, the bomb should be directly below the plane when it lands

After that, the distance of the plane flying horizontally, the distance traveled by the sound diagonally to meet the plane, and the vertical 2000 meters, just forming a right triangle. Use the color strand theorem.

2000 2+(V-FlyX30) 2=(330x20) 2 Solution: V-Fly=210m s

Please click.

The time of the bomb landing is calculated from h=1 2gt 2, and the sound propagation time of t=20s** is 30-20=10s

The sum of the squares of the horizontal and vertical displacements is the distance the sound travels.

30v)^2+2000^2=(330*10)^2v=

Analysis: After the bomb is released, the bomb hits the ground at t1 time, then it is obtained by the formula of flat throwing motion: , let the time elapsed from the bomb ** to the pilot hear the sound of ** t2, then t= t1 + t2 is obtained from the condition given by the question, and the geometric relationship of the right triangle of the figure can be obtained, and the solution is v=262m s.

In this way, the trilateral relationship of the triangle can be expressed by an unknown, here using the Pythagorean theorem: (10v) 2+2000 2=(330*10) 2

h=squared, t=20s

Sound propagation time t=30-20=10s

According to the Pythagorean fixed force (10v) square + 2000 square = (10 330) square.

v=210 meters per second.

Position of the center of gravity. Mass = density multiplied by volume, the unit of volume in the question needs to be converted.

1.The lower end of the thick glass tube with both ends of the opening is covered with a tight elastic film, and it is fixed, and some alcohol is poured from the upper mouth, the membrane will protrude downward, which shows that (the liquid has downward pressure), if it is slowly immersed in the container containing water vertically downward, when the liquid level inside and outside the glass tube is the same, the elastic film will (protrude upward).

2.If two identical containers of A and B contain water and alcohol of equal mass respectively, then their pressure at the bottom of the container f water ( f alcohol, if the two points ab inside the liquid are at the same height, then the pressure of these two points is p( pb

The air does not dissolve in alcohol (uncertain), concave downward, greater than, equal to (if it is the same liquid).

1.The fluid has a pressure protrusion upward.

2.Equals Equals Equals.

Metal volume: 210+

Density 210+ is the mass of the reduction (i.e., the mass of the overflow water) The density of the water is 1 so the volume is 4 1=4

Then the volume of the metal block can be obtained Mass Volume = density.

210 + total mass 1 mass of total mass reduction (i.e., mass of overflow water) The density of water is 1 then the volume of the metal block can be obtained Mass Volume = density.

or volume volume * (x-1) = net increased mass (i.e. mass of metal - mass of spilled water).

The magnitude of buoyancy is only related to the volume of water discharged by the object.

1) False. If the wood pellet floats on the surface of the water, the buoyancy experienced by the wood pellet should be less because it excludes the small volume of water.

2) Right. The volume of water discharged from the submarine has not changed, and the buoyancy has not changed.

3) False. The ship is going to sink, but the buoyancy of the ship is always equal to its own gravity (unless the ship sinks), so it does not change, and the statement "buoyancy becomes smaller" is wrong.

4) Right. The magnitude of buoyancy is only related to the volume of water discharged by the object.

2.Pick the number block C

Since the density of the wood block is less than the density of water and mercury, the wood block must float on the liquid surface, and the gravity is equal to its own gravity.

3.Select BIf the buoyancy is reduced after the bowl sinks, the volume of the water discharged will be reduced, and the water surface will be lowered.

5.The volume of iron should be 1 cubic centimeter.

It should sink in water and alcohol, according to the volume, f water 1n, f sprinkle essence =

v water = 1 cubic centimeter, v sprinkle essence 1 cubic centimeter.

Since the mercury density is not given, it is recommended to calculate the v mercury yourself according to the buoyancy formula

1 Negatively charged.

2 e=20/3

f=mae×q-mg=m×

E to the minus 8 power to the minus 7 power 10 = minus 7 to the power e = 40

(1) The velocity of motion is opposite to the electric field, indicating that the charge is negatively charged.

2) Force analysis: QE-MG=MA E=M (G+

The velocity of motion is opposite to the electric field, indicating that the electric field force is upward, so the charge is negatively charged.