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9. On a construction site, the worker's master uses pulley block to lift an object with a weight of 600N. He stands on the ground and pulls down the rope with a force of 200N, so that the object rises at a constant speed of 3M. The efficiency of the pulley block is 75%. (1) calculate the effective work done by the pulley block to lift heavy objects and the total work done by the worker's pulling force; (2) calculate the number of rope strands n of the starting pulley in the pulley block, And draw the schematic diagram of the pulley block 10. Raise the 400 N object by 0.5 m with a lever, and the dynamic action point drops by 2 M. if the dynamic force is 120 n, calculate the total work, effective work, additional work and mechanical efficiency
9 (1) w useful = GH = 600N * 3M = 1800jw total = w useful / η = 1800j / 75% = 2400j (2) n = w total / Fs = 2400j / (200N * 3M) = 410. W total = FS = 120N * 2m = 240jw useful = GH = 400N * 0.5m = 200jw extra = w total - W useful = 240j-200j = 40J η = w useful / wtotal = 200J / 240j ≈ 83.3%
The problem of physical buoyancy requires detailed formula and steps
A foam board of 54 cm wide, 28 cm high and 3.4 cm is floating on the water, and there are 72 holes with a diameter of 3.1. If we want to immerse the water into 2 cm depth, we should place multiple objects on it.
The mass of floating plate is 90g
At the same time, according to Archimedes principle: F floating = g row = g object, namely: ρ water GV row = g plate + G object, and: V row = sh '= 54 × 28 × 2 = 3024cm ^ 3 = 0.003024m ^ 3, G object = ρ water GV row - G plate
On the formula of physical calculation
Do P = u & # 178 / R and P = I & # 178; R need to be inverted when they are used in calculation? Do they use p = UI to inverted themselves or P = UI and Ohm's law to inverted together?
Your idea is no problem. These formulas are simple. If you can remember them, you can use them directly. If you can't remember them, you can deduce them with UI and Ohm's law. Or you can test them with derivation to avoid mistakes
How to calculate C in physics
If a 20 ohm conductor has 3A current for one minute, what is the charge passing through the cross-sectional area_____ C?
Don't give me the URL, all I want is the answer and the formula
Q=I*t
Charge quantity = current intensity * power on time
The answer to the above question is 180C
The calculation formula of physical echo in grade two of junior high school
s=vt/2
RT I want to understand... I want to use my fill in questions
The main purpose of using echo is to find some distance, such as measuring the depth of the ocean, the distance between valleys and so on. As long as you know that half of the echo time is multiplied by the corresponding sound speed, that is: S = V * t / 2
There is a high cliff in front of the train. The driver hears the echo from the cliff 1.2 seconds after the whistle. If the train is moving at a speed of 72 km / h, how far is the driver from the cliff when the whistle is sounded?
The speed of the train: V1 = 72km / h = 20m / s, according to v = st, the distance of the train in t = 1.2s time: S1 = v1t = 20m / s × 1.2s = 24m, the distance of sound transmission: S2 = v2t = 340m / s × 1.2s = 408M, if the distance from the train to the cliff is set as s when the driver honks, then: 2S = S1 + S2, ｜ s = S1 + S22 = 24m + 408m2 = 216m
Distance formula
Distance = (time × speed of sound) / 2
Speed of sound: speed of sound propagation time: time taken to get the echo
Grasping the skill is the key to learn physics well----
There is a car on the mountain road in front of the cliff. In the following two cases, the car hears the echo after 3 seconds after the car honks. Find the distance between the car and the cliff when the car honks. (air sound speed 340m / s) (1) the car runs at a constant speed close to the cliff, with a speed of 10m / S; (2) the car runs at a constant speed away from the cliff, with a speed of 10m / s
(1) Let the distance between car whistle and cliff be S1, then V sound T1 + V car T1 = 2s1340m / s × 3S + 10m / s × 3S = 2S1, the solution is S1 = 525M. (2) let the distance between car whistle and cliff be S2, then V sound t2-v car T2 = 2s2340m / s × 3s-10m / s × 3S = 2s2, the solution is S2 = 495m
Calculate the formula. But do not know where wrong. Please write clear calculation project
A pendulum, like a floor clock, can rotate 360 degrees. The length of the pendulum is 825mm. The lowest point, that is, the six o'clock direction, is 0 degrees. The pendulum falls freely from the 11 o'clock direction (- 150 degrees). The speed of the pendulum is 6.3 cycles per minute
Instantaneous speed = 6.3 laps per minute * pendulum length 825mm = 6.3 * 2 * pi / 60 * 0.825 = 0.544
The kinetic energy is 0.5 * m * 0.544 * 0.544 = 0.148m
The gravitational potential energy at 11 o'clock is m * 10 * (1 + sqrt (3) / 2) * 0.825 = 18.66 * 0.825mg = 15.39m
Energy conservation, the remaining gravitational potential energy is 15.242m
The height is 15.242m / (10m * 0.825) = 1.8475 = (1 + cos a)
A = 32.0592, that is - 147.941 degree
RELATED INFORMATIONS
- 1. Write detailed process and formula 1. A car honks its horn in front of the mountain and hears the echo after 25s (the echo is 340m / s). If the car approaches the mountain at the speed of 72km, how far away is the horn honking from the mountain? 2. He stood between the cliffs and fired at a certain position. After 1 s, he heard the echo for the first time. After 0.5 seconds, he heard the echo again. Given that the sound speed is 34m / s, what is the distance between the two cliffs?
- 2. The definition of Coulomb's law is the force between two static point charges in vacuum, but since there is a force, will it still be static, and in vacuum The definition of Coulomb's law is the force between two static point charges in vacuum, but since there is a force, will it still be static, and there is no friction and electrostatic force to balance in vacuum. If gravity and electrostatic force balance, it is not a complete case
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