I can t figure out a physics problem

The object at 10m s can be obtained, and t is 2.

then a 5m s.

Displacement 2ax v end - v 0.

Find x 10m

At the end of 2s, f changes by 90°, and it can be seen that the velocity in the original direction remains unchanged for 10m s, and the object moves uniformly in the direction of force for a 5m s.

At the end of 4s, the total displacement meter in the original direction is 10 10 10 2 30m, along the f direction sy 1 2a t 1 2 5 2 10m, according to the motion synthesis of s (sx sy) 10 10m, at this time the object velocity v 10 10 10 2m, so only the c item is selected.

Kiss! It's not easy to look at handmade!

For example, it accelerates to the north for 2 seconds, then accelerates to the east for 2 seconds, and at the same time, the speed to the north remains the same, and the speed is 10 meters north, and then the speed is maintained for another 2 seconds, 20 meters, a total of 30 meters.

Walked 10 meters to the east, so 10 meters under the 10 roots in the northeast corner, the speed is 2 meters under the 10 roots.

The decomposition of the movement, the movement at the beginning of 2S is the synthesis of the two movements, c, the distance of the wooden block is 10 meters under the 10 roots.

is to rotate the force instead of disappearing the constant force yields a=5m s2 which is equivalent to an object with an initial velocity being acted upon by only one force, i.e., a flat-like motion.

In the first two seconds, you can find a by doing a uniform acceleration motion, and then you can find a by doing a flat throwing motion, and the acceleration is a, and then you can find it.

It's just that the direction of the force has changed, and the magnitude hasn't changed, so it's better to do a uniform acceleration, and think about it, don't turn the horns.

AD is the distance of motion of the boat when AB is in motion, AE is the distance of motion of the boat when AC is in motion, and AD is > AE

The result, of course, is a shorter voyage along the AC.

The analysis is slightly more complicated, mainly doing parallelograms.

The velocity of the water and the velocity of the boat in still water are the two adjacent sides of a flat quadrilateral, and the diagonal direction between them is the actual direction of the boat's motion.

The limiting conditions of the drawing are: the size of the water flow velocity and the determination of the direction;

The speed of the boat movement is determined; Determination of the actual direction of movement; It is equivalent to the parallelogram that one adjacent edge has been determined, the size of the other adjacent edge has been determined, and the diagonal direction of the sandwich is determined.

Draw a parallelogram and compare the length of the diagonal lines and their weight perpendicular to the river bank in both cases.

FB is the frictional force between the B plate and the ground.

The first step is to find the friction force of the three boards together on the ground, and the friction force f = mgu because the sliding friction factor u and the gravitational acceleration g are unchanged, so the ratio of the friction f between the board and the ground is equal to the ratio of the mass m, you can find the friction between each board and the ground (the mass of the B board accounts for 1 4 of the total mass of the three boards of ABC, that is, the friction of B is 1 4 of the total friction).

The second step is to analyze the force on the horizontal plane of the B plate. The frictional force fb (the direction is opposite to the direction of movement of the B plate), the thrust (pressure) of the A plate to the B plate (the direction is perpendicular to the AB contact surface), and the static friction between the AB.

On the whole, the friction and thrust of the plank are equal, and in this problem, the friction is proportional to the area (because the area is proportional to the mass) The area of b is the total area, so fb is, and then the resultant force is zero, and the nine balls come out.

Hello classmates, first of all, it can be seen from the question that in the whole process of motion, the three wooden blocks did not move relatively, which can be understood as a temporary whole, f is the external force received by the object, and the friction received by the physical movement is equal to the opposite direction, and then the problem solves the pressure between a and b, and it is necessary to analyze the force of a or b alone, because a analysis should consider the role of c, and gu analyzes b alone, at this time, there is an internal force between a and b, and the manifestation of the internal force is the interaction force between a and b. Maintain B relative to A without moving, that is, the reverse equilibrium force of the support force and the resultant force of Fab. Hope to adopt, thank you! If there is any uncertainty, please ask.

1) The total time it takes for the child to fall first

According to the conditions of the question, the height of the window sill on the 10th floor from the ground is h 9*3 1 28 meters.

Obtained by h g*t 2 2.

28＝10*t^2 / 2

t root number seconds.

It can be seen that Wu was originally downstairs, so his reaction time was allowed to be about seconds at most (generally considered seconds).

2) Let the desired velocity be v

Obtained by v 2 2gh.

v^2＝2*10*28

Get the V root number 560 m s

1) Wu's reaction time is the time when the child falls, and the distance between the child and the ground is.

x=(3×9+1)m=28m

From x=gt2 2, substituting the data to get t=

2) When the little girl is about to land, the speed v=gt=.

Before Niuniu landed, a total of 1+3*(10-1)=28m1 2*g*t=28 fell

t = 56 (1 2) = 2 * [7 (1 2)] seconds.

The velocity when about to land is v=gt=2*[7 (1 2)]*10=20*[7 (1 2)].

Total height = 8 * 3 + 1 = 25 meters.

Reaction time = 25 * 2 10 = 5 sec.

Speed = 10 5 m sec.

1.The fall distance is 28m, which is determined by the formula of free fall, ,t=;

The reflection time is the time from free fall to the ground, the speed from free fall to the ground, and the distance and acceleration can be obtained.

From a power point of view:

The thicker the thermally resistive conductor, the greater its conductivity, the smaller the resistance, and the greater the power consumption. （p=i^2*r=u^2/r）

In terms of the principle of lamps.

The new energy-saving lamps are different from the traditional electric thermal resistance lamps in that the energy-saving point uses a high voltage to [ignite] a highly active gas (excited electrons to produce high-cycle electromagnetic waves called visible light to the human eye) to produce light, and then uses microcurrent to keep the gas active to continuously emit light, so it does not emit a full chromatography fiber like conventional lamps and is accompanied by a large amount of heat. There will also be no metal conductor wires directly attached to the two stages and the entire lamp. (The conductor of which is the gas inside the lamp) Question 1:

The filament is the main component of the bulb to emit light, and in the case of constant voltage, the larger the current, the greater the degree of heating and luminescence of the filament, but the current that the filament can pass through is proportional to the diameter of the filament, so the thicker the filament, the greater the current that can pass, and the filament of the 5w bulb must be much thinner than the 40w filament, which can be observed with the naked eye.

Question 2: electric power = voltage x current, according to this formula, our household electricity voltage is 220v, which is a constant, the current of the nominal 5w bulb should be 5 220 = ampere that is milliampere, 40w bulb current should be 40 220 = ampere that is, milliamp, through the measurement of the bulb current, you can distinguish this is a 40 watt bulb or a 5 watt bulb.

Answer: (1) The power of the 5W bulb is small, and the resistance should be large when the voltage is the same as 220V, so the resistance wire should be relatively small (the smaller the resistance wire, the greater the resistance.) From p=u 2 r, u is certain, and the larger r is, the smaller p is. , so it is said: the filament of 5W should not be so thick;

2) Principle: From p=ui, the junior high school student takes the bulb to the repair shop to measure the current, and knows that the electricity voltage of domestic residents u=220v, and the electric power p can be obtained by using the formula.

The words of floating are on the water, with part exposed, part underneath; If it's levitated, it's in the water.

According to the buoyancy formula, if it is completely immersed in water, the buoyancy force is 6N, which cannot be balanced and will float.

So, there will be 1 to 6 blocks on the outside, which is floating.

The gravitational force is less than the buoyancy force when levitating.

The density of the object is its weight divided by its volume, and its density is less than that of water, so it floats.

That is, the density of the object is less than the density of water, so it will float on the surface of the water, and if the density of the two is equal, it will be suspended.

I know.. When an object is floating in the water and is at rest, buoyancy = gravity is very simple. Suspension is not on water. It is possible to be in the water. There is pressure.