Urgent solution of high school physics problem 20, urgent solution of high school physics problem

Hey, it's not good to know that, it's too hard to input math symbols and letter symbols......

Solution: (1) Let the maximum angular velocity of a and b when the two objects and the disc do not slide is , and the relay force of the thin wire is t, according to the centripetal force formula f=m 2*r

For a object, it can be listed: m(a)*2*

For B objects, you can list: m(b)*2*(

From : =(4* 10) 3(rad s) so when the angular velocity is 4* 10) 3, the objects A and B do not slide relative to the disk.

2) When the rotation speed of the disc increases to A and B, when the two objects are about to start sliding, the thin wire is burned, and the B object will fly out of the disc due to the loss of the tensile force of the thin wire; The frictional force experienced by the object a is the centripetal force experienced by it at this time, i.e.: f(a)=m(a)*2*

Hope it helps!

After seeing this kind of problem, you must first set the unknown, then set the acceleration time t, and then analyze --

The difference between the two cars at the beginning of the same phase is 84 meters, and finally they meet, indicating that the displacement of A is 84 more than B in this process, so it is necessary to write the displacement of AB in this process: according to the known conditions and the learned formula, we can know that XA = 12 * 20 = 240M, XB = V0T + at 2 2 + (12-T) * VO, bring in the data to get XB = T 2 + 48, now you can list the equation: XB + 48 = XA, bring in the XA and XB I just listed to solve the equation In the end, we get t=12, so the acceleration time is 12s ps:

If there is a question that you don't know or what I said you don't understand, oh oh, just look for me, willing to serve, introduce, even a new high 2 drops, great love physics hehe、、、

V-t diagram to solve. The enclosed area is the displacement.

s=v1*t+s0=20*12+84=324v2*t+(a*t2*t2)/2+(v2+a*t2)*(12-t2)=s

Got:t2= ?

After calculation, there is no solution to this problem!

Instant healing accelerates, with a final velocity of 28. This cannot be established.

The first question should be asked, right? No follow-up questions.

The second question is to use the acceleration obtained by the first question, because the question stem says that the braking acceleration remains unchanged, so the braking acceleration of the D-shaped train is still the original value, so the second question is to ask the D-shaped train from a speed of 200km h to 0 through the displacement 2as=v0

The third question is to ask how much time does it take for a D-shaped train to slow down from 200 km h to 0 s=1 2at

If you don't understand, please ask.

This one is about acceleration.

a=-4 1 m s square.

a=-12 1 m s square.

Since the acceleration is different, x=v0+ square is used.

Find =6m =2m

There is no "size" in the same direction, take a=-4m s square.

Hence 6m

There are two cases, in the same direction: the average velocity is 8 + 4 divided by 2 = 6, and the displacement is 6 m

Reverse: The average velocity is 8-4 divided by 2=2, and the displacement is 2m

Motor movement is most likely the first case, which is 6; There is no size, indicating the direction of the speed is the same, in the first case, 6m.

Reference. A swimmer against the current, when passing through a bridge hole, the kettle was lost, and when he found it, half an hour had passed, and he looked back and found it 1km away from the bridge hole, so what is the speed of the water flow? (Set up a kettle that can float on the surface of the water and move with the water after leaving the human body).

Solution 1 Let the speed of the swimmer in still water be v people, the speed of the water flow is v water, the time from the bridge hole to the time when the swimmer finds the kettle lost is t1=1800s, and the time it takes for the swimmer to find the kettle from looking back to finding the kettle is t2Rule.

v person - v water) t1 + v water (t1 + t2) = (v person + v water) t2 = 1000 can be obtained.

t2=t1=1800s, vwater=s (t1+t2)=

Solution 2 Because both the human and the kettle drift downstream with the water, and the speed of the downstream drift is equal to the water velocity, the distance of the person and the kettle drifting downstream in the same time is the same. In this way, we assume that the water does not flow, then the kettle will not move at the bridge hole, and the person swims upstream at a speed in still water for 1800s, and when he finds that the kettle is lost, he has left the bridge hole and swam upstream v person 1800 (m), and when he returns, he swims the same distance back to the bridge hole, then the time to return to the bridge hole should also be 1800s. That is, people swam together for 3600s

At this time, the water is considered to be flowing, then the kettle swims 1000m in 3600 s, so the speed of the water flow is v= m s = m s

Since it glides at a constant speed on a rough inclined plane, the force is balanced in the direction of the inclined plane.

In this direction, a gravitational force is applied downwards along the inclined plane f=mgsin30 and a frictional force upwards along the inclined plane f=umgcos30 (because it moves downward relative to the inclined plane).

So f=f=1*10*

1.Slide at a constant speed, so the force is balanced.

2.The equilibrium of friction and gravity in the horizontal direction of the inclined plane is that f=sin30mg=1 2x1x10=5n direction is parallel to the inclined plane.

This problem uses the symmetry of the motion of the free fall, and the ascent process passing through the high window can be seen as the same time it takes to descend through the window.

Solution: Draw a diagram with the velocity of passing through the upper edge of the window during descent as v1 and the velocity of reaching the ground as v2, t1=, t2=. According to the displacement formula:, the solution is v1=15m s.

According to the velocity formula: v2 = v1 + g (t1 + t2) = 18m sAccording to the formula of free fall motion: h=(v2)2 2g=answer:

Homogeneous acceleration phase: a=

The time to accelerate to 4m s is 10s, the displacement is 20m, and the remaining 5m is the phase of constant motion, time t=5 4=so the total time.