Speed by physical calculation Throw a ball horizontally at a speed of 15m / s at a height of 20m, and calculate (G is 10m / S2) regardless of air resistance (1) The speed of the ball at 10m above the ground (2) The speed at which the ball lands

Speed by physical calculation Throw a ball horizontally at a speed of 15m / s at a height of 20m, and calculate (G is 10m / S2) regardless of air resistance (1) The speed of the ball at 10m above the ground (2) The speed at which the ball lands

one
Work done by gravity
1/2MV^+MGH=1/2Mv^
V is the initial velocity, 15 h is the height change, 10
We get 17 under the root sign of V = 5 *
2. Use the same method, but the change of H is 20
We get v = 25

The speed of physical calculation is on-line
The pulley block is used to lift a 150n heavy object at a constant speed. The pulling force is 300j (excluding the pulley weight and friction). How much pressure is used? How high can the heavy object be lifted? The pulley block has 4 strands of speed online

F=1/4G=37.5N
W = FS s = w divided by F = 8 (m)
Lifting weight H = w divided by 150 = 2 (m)

A physics problem -- speed calculation
Gary needs to solve a problem about time, distance and speed, but he forgot the formula. The conditions given in the problem include M / s and km, which require a measurement value in S. what Gary needs to do to get the answer is ()
A is m / s times km, then 1000
B divide M / s by km and multiply by 1000
C is divided by M / s by km and then by 1000
D is m / s times km and divided by 1000

A m/s*km*1000=1000000m^2/s
B m/(s*km)*1000=1/s
C m/(s*km1000)=1/(1000000s)
D m/s*km/1000=m^2/s
Choose B

Students a and B measured the propagation speed of sound in the steel. They stood at both ends of the rail 500m apart. A knocked on the rail with a hammer. B put his ear on the rail and heard the sound twice with an interval of 1.37s
(1) Find the speed of sound in steel
(2) The shortest time interval between two sounds that can be distinguished by human ears is 0.1s, so at least on how long rails do these two students have to carry out experiments to measure the propagation speed of sound in steel?

1. Obviously, sound travels fast in the track, so the first sound comes from the track, and the second sound comes from the air
Let v be the speed of sound transmission from the track
500 / 340-500 / v = 1.37 (500 / 340 is the time for sound to travel along the air, 500 / V is the time for sound to travel along the rail)
The solution is v = 5000m / s
2. According to the above solution:
Let the rail length be L
There are: L / 340-l / 5000 = 0.1
The solution is L = 36.6m

Proof 3A ^ 2 (B-A)

On the mean value theorem, it is proved that when a > b > 0, 3b ^ 3 (a-b)

Let f (x) = x ^ 3, then f (x) is continuous on [b, a], and (B, a) is differentiable, and f '(x) = 3x ^ 2

If 3A = 3b, then a of B = ()

3A = 3b, then a of B = (1)

Can we get a = B from 3A + 1 = 3b-1? Why?

No
Because 1 is not equal to - 1

Can we get a = B from 3A + 2 = 3B + 2? Why?

Can get
Because 3A + 2 = 3B + 2, if you subtract 2 from both sides, 3A = 3B
At the same time, a = B

If A-B = 5, then 3A + 7 + 5b-6 (a + 13b)=______ ．

3A + 7 + 5b-6 (a + 13b), = 3A + 7 + 5b-6a-2b, = - 3A + 3B + 7, = - 3 (a-b) + 7, = - 3 × 5 + 7, = - 8