30 physics questions for the winter vacation of junior high school, physics questions for the winter

It's very simple, method one:

Take a bottle of water and put it in the cabin.

If the water is shaking, then the ship is in motion.

Otherwise, it is static.

Because there must be vibrations when the engine starts, and the deck of the cabin can transmit the vibration of the engine.

Method 2: Take a level fixed on the deck, observe the pointer of the level, if the pointer of the level is constantly swinging, it means that the ship is moving, otherwise it is stationary. Because if the boat is exercising, it is impossible not to shake. (provided there is no wind and no waves).

Method 3; Take a GPS locator and fix it on the deck, ** on it is a number, if the number changes, it means that the ship is in motion, otherwise it is stationary. Because if the boat is moving, the longitude and latitude of its position will change.

There are many, many ways to do it, and you can think about it yourself. (The answer on the 1st floor is incorrect) Explanation: There is no absolute motion and rest of any object, only relatively speaking, there is motion and rest. The above answer is just our general opinion.

You can check out the knowledge related to junior high school physics.

You can hold a ping pong ball in your hand, the person stands upright, holds the ball, holds the ball in your hand and lifts it high, and then lets go of your hand, the ball will fall, if the ball falls vertically, then the boat is stationary, but if the ball falls in a parabolic curve, then the boat is moving.

Upstairs is not right, objects have inertia.

No, the one on the first floor doesn't understand physics!

The apple is subjected to downward gravity and upward resistance in the air, and the resultant force = g-f

d can make a force analysis, very simple.

This problem is easy to solve.

It should be gh+g s

Well, it's hard to understand that method, so I'll tell you another method, create your own!

First of all, separate the water from the piston, first calculate the pressure of the water on the bottom of the container, which is PGH, and then, you think, how does the piston float? It is the upward buoyancy of the water to the bottom of the piston, this buoyancy is equal to the gravitational force (the piston weight is not counted), lz should know that the action of the force is mutual, so the piston also gives the water a downward reaction force, where does this force go? It becomes the water to the bottom of the container, which is GS

So, the force at the bottom of the container is the addition of the two forces, which is gh+g s, understand?

If you don't understand me, I'll give you an answer.

Completely hand-to-hand .........

This is characteristic of liquid pressure and is only associated with high and liquid density.

So it should be PGH

If it is a junior high school question, it should be the same. When the wood is in the boat, the buoyancy provided by the water is the gravity of the wood + the boat, and when the wood is in the water, the buoyancy provided by the water is still the gravity of the wood + the boat, so the volume of the water discharged remains the same, so the height of the water surface remains the same.

In addition, strictly speaking, the water level should rise. When the wood enters the pool, the surface area of the pool is reduced accordingly (assuming the boat occupies the same area), so that the depth of the water is deeper for the same volume of water discharged, and therefore the height of the pool is slightly higher.

Option c The displacement is related to the total mass of the ship and the wood, and the total mass of the boat and the wood does not change.

c, wood will float on the surface of the water when thrown into the water, which has the same effect as before.

c Because the buoyancy of the wood when it is placed directly in the water is not changed from when it is in the boat, the buoyancy is only equal to its own gravity, so there is no difference between taking it out and throwing it into the pool and when it was originally on the boat, and if the question is given a stone, the height of the water surface is different.

Question 1··· The power of 105W can't make 100kg of water spray 80 meters per second The question is wrong, it feels like it should be 105 kilowatts, and the useful work is 80*100*10*60=4800000j, and the total work is 105000*60=6300000j, and the mechanical efficiency divides them by =4800000 6300000 *100%.

The second problem is to use the impulse theorem to explain f (average force) * t = 0-mv mv is a fixed value: t is large on the beach, f is small (t is big because there is a buffer).

T is small and F is big on the cement road.

2) It may be that the sand structure is soft, the contact area with the egg is larger, and the gravity of the egg g is certain, so the pressure is less and it is not easy to break.

When pulling up: f=2f+g=; So 2f=;

When pulling down: f'=2f-g=;

So that's it.

Kinetic friction consumed by pumping upward=

The sum of the force and gravity required to pump from below needs to be greater than the frictional force f+g

So f

Hehe, you're not taking into account the effect of friction here

From the upward pull, it can be concluded that the maximum friction is , and the direction is downward.

When pulling downward, the maximum friction force is also the same, and the direction changes to vertical upwards. In this way, gravity cancels out part of the force to 1g, and the rest is the pulling force.

It is a matter of listening to the direction of the force. When pulling upward, the direction of its friction force is opposite to the pulling force, downward, it can be calculated that its pulling force is , when pulling a from below, the friction direction is upward, and its large i is the same, so that the minimum pulling force pulled out from below should be.