How do you know each option in this physics problem?

Hello, I majored in physics in college and would love to help you.

See below for an analysis of each option.

Option A: Ascending at a constant speed, there is no force between A and B, and object B is subjected to three forces, including its own gravity, the force on the surface of the conveyor belt, and the upward friction force. The resultant force of the three forces is 0So option A is correct.

Option B: Uniform acceleration upward, there is a force between A and B, and object B is subjected to four forces, including its own gravity, the force on the surface of the conveyor belt, the force on object A, and the friction force. The resultant force of the four forces is not 0, which causes b to produce an acceleration.

So option b is correct.

Option C: After an abrupt stop, there is no force between A and B, and object B is subjected to three forces, including its own gravity, the force on the surface of the conveyor belt, and the downward friction force. The resultant force of the three forces is not 0So option c is wrong.

Option D: After a sudden stop, the friction on object b is the component of the vertical slope of its gravity multiplied by the coefficient of friction, and the magnitude is not greater than the original, but in the opposite direction, along the inclined plane downward. So option d is wrong.

To sum up, the correct option is (ab).

When reading the problem, objects A and B are of the same material, indicating that they have the same friction coefficient and different mass and magnitude, indicating that the friction force generated by the bevel is different for them, and the friction force of A is greater than that of B. This is the key to solving the problem. The specific thought process is a bit complicated, so I won't go into detail here.

Please refer to the attached drawings for a schematic analysis of the forces for each option. Hope it helps

Option A: If B moves upwards at a uniform speed, then it proves that B is now in equilibrium, and if B is only supported by gravity and the inclined force, it is impossible for it to maintain a constant velocity, so it must be subject to a third force, which is the frictional force between the inclined plane and B, and the direction is upward along the inclined plane.

When it is 0, combined with the original diagram, it can be seen that r=0, that is, there is no component mg*tan =0 in the horizontal direction, and no circumferential telemotion is made (at this time, it can no longer be expressed by mg*tan =mr), so w=0

The following is combined with g l*cos = to obtain the result of choosing b

I don't understand, then hi me].

a.That's right. The AB plate is grounded, and the electric potential is always zero. Moving from A to N, the electric potential remains unchanged.

b.Mistake. If the potential at point m is greater than zero, the metal plate will generate an induced charge, which will produce a field strength, making the field strength at point m greater than this.

c.That's right. If the electric potential is a zero pair, the field strength is not zero, and the vertical ab points to p.

d.Mistake. C is correct, D is wrong.

A young man carries a bucket of water in his right hand, weighing 20 catties, and a fish in his left hand, weighing 1 catty, and the specific gravity of the fish is the same as that of the water. What is the force of carrying the bucket?

The net weight of the fish has not changed, it is still 1 catty, kilogram. The fish is put into the water, and the total amount of fish water is 21 catties, 21 * kilograms.

If the bucket is carried alone, then the force on the hand is equal to.

At this time, the weight (force) of the fish is 0, and the mass is 1 catty (, and the force of carrying the bucket is.

The mass of the fish will not change, it is still one catty, the fish floats in the water, the gravity and buoyancy are equal, and the net force of the fish is zero. The literal meaning of net weight should be mass, so it is still a catty.

The barrel and fish weigh 21 pounds together.

b c is wrong, the kinetic energy and potential energy of the molecule have nothing to do with the motion of our body itself, the change of position, as for the temperature of the object.

In addition, everything that moves has kinetic energy, and molecules are no exception.

So the answer is A

a Correct.

Only kinetic energy can be achieved when an object moves, while molecular potential energy and molecular kinetic energy belong to molecular internal energy, which is not a concept and has no direct relationship with the potential energy and kinetic energy of an object

A right. Regardless of whether the object is moving or not, the molecules are always moving irregularly and have kinetic energy.

The molecular potential energy is unchanged. Here the macroscopic motion has no effect on the molecular potential energy because there is no change in the structure of the object. So B is clearly wrong.

c error. The velocity of the object increases, but the kinetic energy of the molecule does not change.

Possible. Velocity is a vector, so it's going to be discussed by category here.

1. When the velocity at the beginning and end is in the same direction: the velocity at the midpoint of time is 7 meters per second, the displacement is 7 meters, and the acceleration is 6 meters per square second;

2. The initial and final velocity is reversed, and the initial velocity is positive, then a = -14m s, and the displacement x = 4 + m at this time the acceleration is 14 meters per quadratic second, greater than 10 meters per quadratic second.

The question gives the velocity magnitude, so the possible change in velocity is 14m s

So the answer D is right.

A and D are both correct.

Acceleration is an acceleration motion or it may be a deceleration motion.

The acceleration is 6m s2When slowed down, it's 14m s2

There are two cases: the direction of the velocity does not change and the velocity has reversed after 1s.

Choose A, D

d can be a velocity equal to 4m s in the negative direction, and 10m s in the positive direction after 1s, so the change in v is 14m s in 14m, so a=14m s 2 > 10m s

a That's right.

dWhoever is subjected to the force, on whom the point of action is on.

The force of the hand to the bucket and the force of the bucket to the hand are a pair of acting and reacting forces, equal in magnitude and opposite in direction, the points of action are on different substances, and the lines of action are on the same horizontal line.

In the question, the hand is forced, so the action point is on the hand.

The force given by the hand to the bucket is upward, so the force given by the bucket to the hand is downward.

d is not difficult to analyze:

The hand is subjected to downward force, which is applied by the barrel, and the point of action is on the hand;

The barrel is subjected to two forces, upward by hand and downward by gravity, both of which are on the barrel.

dWhatever is forced, the point of action is on what object.

D should be chosen

The force is mutual The bucket guards the gravity, and the gravity is downward, then the force exerted by the bucket on the hand should be downward. To analyze the force exerted on the hand, then the point of action is on the hand.

So, a bc is all wrong! ~

The force on the D hand is, of course, downward and is not explained.

The point of action is to look at the place of contact, of course, on the hands.

Exclusion method option C

The speed of sound is related to temperature, and the speed of sound in air at 15 degrees Celsius is 340The temperature is high and the speed of sound is high. There is a sonic velocity meter.

B should be 30.

d20——20000

The speed of propagation is related to temperature.

Amount. First force analysis, mg=n, f=un=umg, according to Newton's second law a=(f pull-f) m,, the simultaneous solution gives u=