Additional bounty of 30 High School Physics

Velocity], vector, with direction This is the state quantity that represents the state at a certain moment The state at that moment, plus or minus means relative to the reference direction, the same is positive, and the difference is negative.

Velocity], a scalar quantity, is the same as velocity, but there is no direction, there is no plus or minus, and it is as much as it should be

Acceleration], vector, as the name suggests, is the increment of velocity, in the variable speed motion, which represents the change in velocity at this moment, and its plus or minus does not mean that making the velocity greater is positive, and making the velocity smaller is negative, but according to the force, which is the same as the direction of the resultant force.

Average velocity], a scalar because it is not a state quantity, represents the average value of velocity over a period of time, and solves with a +- sign of velocity.

Average Rate], scalar The average size of the rate over time, the average of the +- sign size without velocity.

Instantaneous velocity], instantaneous velocity is velocity.

Velocity describes how fast or slow an object is moving, including average velocity and instantaneous velocity.

Average velocity Bit removal in time Initially describes how fast or slow an object moves in a period of displacement.

Instantaneous velocity accurately describes how fast or slow an object is moving in a certain position.

Velocity The magnitude of the instantaneous velocity.

Average velocity The ratio of the distance traveled by an object to the time it takes to pass through this distance is called the average velocity on this distance, which is customarily called average velocity, but it is very different from the average velocity. The average velocity is the ratio of the displacement passed by the object to the time taken to pass through that displacement.

Velocity], vector, with direction This is the state quantity that represents the state at a certain moment The state at that moment, plus or minus means relative to the reference direction, the same is positive, and the difference is negative.

Velocity], a scalar quantity, is the same as velocity, but there is no direction, there is no plus or minus, and it is as much as it should be

Acceleration], vector, as the name suggests, is the increment of velocity, in the variable speed motion, which represents the change in velocity at this moment, and its plus or minus does not mean that making the velocity greater is positive, and making the velocity smaller is negative, but according to the force, which is the same as the direction of the resultant force.

Average velocity], a scalar because it is not a state quantity, represents the average value of velocity over a period of time, and solves with a +- sign of velocity.

Average Rate], scalar The average size of the rate over time, the average of the +- sign size without velocity.

Instantaneous velocity], instantaneous velocity is velocity.

According to the principle of leverage, herbivores mainly act on the front, and carnivores mainly on the rear;

Because herbivores t = 10m, it can be considered that t>>m, so the posterior muscles exert a lot of force, so they have to overcome a very long force arm, so they must mainly act on the front part; Because carnivores t=m2, the posterior muscle force is very small, so the force arm to overcome must be very short, so it mainly acts on the posterior.

Please tell us the size of the angle shown in the diagram and the angle between t and horizontal.

Front, well, maybe there are a lot of factors that go into it, but that's just the topic.

Because the ice was tied with a rope before melting, the tension on the rope disappeared after melting, and the force on the scale increased before melting Rope tension = ice gravity - buoyancy Bench scale indication = beaker and alcohol gravity + buoyancy During melting The volume of the ice becomes smaller, and both gravity and buoyancy become smaller. Because of the density of water, ice, and alcohol, the gravity of the water The buoyancy of the ice, that is to say, when the buoyancy of the ice changes, the gravity of the water becomes larger, and the speed at which the gravitational force becomes larger The speed at which the buoyancy becomes smaller, so the final scale becomes larger.

After thawing Rope tension = 0 Weighing number = beaker and alcohol and water gravity Ice becomes smaller in volume and the mass remains unchanged after melting. You can also think of ice as a stone, first tied with a rope and then cut the rope so that the scale increases the gravity of the stone and becomes larger.

Quite simply, the liquid gives the ice cube an upward buoyant force, and the ice cube definitely gives the object a downward pressure. The buoyancy becomes larger, the pressure increases, so the indication becomes larger. When the ice melts, the buoyancy becomes less and the indication becomes smaller.

Question 1: The frictional force of a small block is its driving force, f=umg, a=ug=2 The velocity v at relative rest = at=2t

The trolley A1 = (f-umg) m=0, the trolley has a constant velocity before the two are stationary, and v = 2;t=1 x matter=;

x-car=vt=2; l = x car - x object = 1

0-1s: x object 1=1

1-2s: The object is relatively stationary, and the whole method f=(m+m)a a=; x object 2 = vt + 1 2at = 2+

x = x object 1 + x object 2 =

The measured time from seeing the enemy plane dropping the bomb to seeing the skinless bomb** is seconds, so t=10s flight altitude h=1 2gt 2

M500m is then initially the horizontal distance of the aircraft from the person s1

500/tan30

500*3 500 times the root number of the servant three).

After flying over the top of the person's head, the time difference is 2s, that is, the distance after flying over the top of the person's head is s2680ms=s1+s2=680

Since the horizontal velocity of the aircraft and the bomb is the same, v=s t=68+50*3 m s=m s

The diagram is missing, but it can still parse the options. First of all, the car and the block are relatively stationary, so the movement of the car is the same as the movement of the block. Therefore, as long as you analyze the state of the block, you can know the state of the car.

As you know, there are only two forces in the horizontal direction, static friction and elastic force. The elastic force must be kx, the frictional force may be 0 umg, and the direction may be left or right, determined by the state of motion (acceleration).

option a, because mg is less than kx, the spring is in a compressed state (the elastic force is relatively large, and there is always it), so no matter what the friction force is, the resultant force must be in the direction of the spring recovery, so the acceleration of the block must be in the same direction as the elastic force, and the acceleration of the trolley is the same (if a is right, you can launch the figure spring of the problem must be on the right side of the block).

b option, the minimum acceleration is the minimum net force divided by the mass, which is (kx-umg) m, but acceleration to the left does not necessarily mean acceleration to the left, it may also be deceleration to the right.

c option, because mg is greater than kx, it may be 0 umg, and the direction may be left or right. When the friction force is in the same direction as the elastic force, and the specific elastic force is larger, the acceleration is opposite to the elastic force, and when the friction force is in the same direction as the elastic force, the acceleration is in the same direction as the elastic force. So the direction of acceleration is possible on both sides (the frictional force is determined by the state of motion).

Option D, the same as C, if the two forces are reversed, the resultant force is the difference between the two forces, so when the car moves at a constant speed, the acceleration is zero, and the elastic force is equal to the friction force, so the minimum value of acceleration is zero (equivalent to the object is placed on a stationary rough ground, and the object is also stationary).

To sum up, because the frictional force is determined by the state of motion (acceleration) (the resultant force provides the acceleration) and is variable.

You can first assume the acceleration, whether the thrust reverser friction and elastic force can be established.

Finding the maximum value of a physical quantity can make the friction force a special value. Maximum, which is equal to mg, is directed to the left or right. Either make the friction equal to the elastic force, or the friction equal to zero. You can calculate some of the best values.

This diagram is missing... You can only guess the diagram by following the options.

First of all, UMG is the maximum static friction force, and KX is the elastic force of the spring.

Less than kx, UMG regardless of left or right, the resultant force of the block must be to the left, and the trolley and the block are relatively stationary, so the acceleration direction of the trolley must be to the left, A is correct.

Less than kx, the minimum acceleration of the car is required, that is, the block receives the smallest resultant force, so UMG and KX are reversed, the resultant force is kx-umg, and the acceleration is (kx-umg) m, so the minimum value is correct, but at this time, it can only be determined that the acceleration is to the left, and it is not certain that the car is accelerating to the left, or it may be to decelerate to the right, B is wrong.

is greater than kx, due to the uncertainty of the direction of friction, the resultant force on the block may be to the left or to the right, so the acceleration of the car can be to the left or right, c is correct.

d.When UMG is to the left, the maximum net force on the block is up to UMG+KX, and the maximum acceleration is (KX+UMG) M, and when UMG is to the right, the minimum net force on the block should be 0 (when UMG=KX), so the minimum acceleration should be 0, D is wrong.

When the spring is compressed, the block has a tendency to move to the left, but if the block is accelerating to the left, and the acceleration = kx m, then the force analysis of the block at this time, the block is not subject to static friction, when the acceleration to the left >> kx m, then the static friction force must also be to the left, so that the block can have such a large acceleration.

This problem, to put it simply, you can think like this, now the block is affected by the force of the spring kx, and then if the car is accelerating to the left, and the acceleration 》kx a, then for the block the car is moving faster than itself, UMG is actually pulling the force of its own movement to the left, I don't know if you understand this explanation?

UMG stands for maximum static friction.

Because the block only collects two forces in the direction of motion, i.e., elastic force and frictional force, if the maximum static friction force is not enough to balance the elastic force, then the block must have a corresponding acceleration in the direction of returning to the original length of the spring, a is correct.

Because friction is motivated, if the elastic force and friction force are reversed, then the block will accelerate in the direction of friction with a small acceleration, and if it is in the same direction, the block will accelerate in the direction of the resultant force with a large acceleration.