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In Baidu RT triangle ABC, angle c = 90 degrees, angle a = 30 degrees, AC = 2
There is a very important conclusion in a right triangle whose angle is 30 degrees: the right angle side of 30 degree angle pair is half of the oblique side, so we can set AB = x, then BC = x / 2. According to the Pythagorean theorem, the square of x = 2 + the square of (X / 2), x = 4, root sign 3 / 3 is obtained. The correct form of the answer is shown in the picture
In the triangle abcz, ab = BC, CoSb = - 7 / 18. If the ellipse focusing on a and B passes through point C, the ellipse is eccentric
Let AB = 2c, then AC ^ 2 = (2C) ^ 2 + (2C) ^ 2-2 (2C) (2C) CoSb,
AC = 10C / 3
According to the question design, 2A = Ca + CB = 10C / 3 + 2C = 16C / 3
The eccentricity of ellipse e = C / a = C / (8C / 3) = 3 / 8
As time goes on, the angle between the acceleration and the velocity direction of an object moving in a constant velocity curve will be () A. May increase B. It must be reduced C. Must increase D. It is impossible to judge the change
The velocity is decomposed in the acceleration and the direction perpendicular to the acceleration. It can be seen that the velocity is constant in the vertical direction and increases in the parallel direction. Then the tangent of the included angle is equal to the ratio of the velocity in the vertical direction to the velocity in the parallel direction. When the velocity in the parallel direction increases, the tangent value will decrease and the angle will decrease
Therefore, B
An object moving along a curve must have an acceleration, and it must be uniformly accelerated. Is that right?
The condition of curvilinear motion is that the resultant force and velocity direction are not in a straight line, so the resultant force must not be zero and there must be acceleration
It's right that there must be acceleration when an object moves along a curve
It's not true that the motion is constant when the force is constant
In curvilinear motion, can acceleration be constant? Can curvilinear motion be uniform acceleration? What is uniform acceleration and what is variable acceleration? When a particle moves in a plane with a certain initial velocity and applies an acceleration which is not in the same line with the initial velocity, will the particle uniformly accelerate along the acceleration direction after a long enough time?
In curvilinear motion, can the acceleration be constant? Yes, such as horizontal or oblique throwing
Can curve motion be uniformly accelerated? Yes, the motion with constant acceleration is uniform acceleration motion, which is also applicable to horizontal throwing motion and oblique throwing motion
What is uniform acceleration? Motion in which the magnitude and direction of acceleration remain constant
What is variable acceleration? The magnitude or direction of acceleration has at least one motion that keeps changing
Curve motion is a variable speed motion. Does acceleration change
The acceleration must change
Because the acceleration is a vector, the direction of the curve motion is constantly changing, so the direction of acceleration is constantly changing, so the acceleration is constantly changing
If it doesn't change, it will do linear variable speed movement
What is the magnitude and direction of acceleration of uniform velocity curve? Do you have a fixed concept about the direction of the acceleration of the uniform velocity curve motion? How to calculate the acceleration?
The direction of acceleration is the same as that of the resultant force, a = f / m, that is, the resultant force divided by the mass
How to calculate displacement in velocity time image
Find the starting point and end point of the time period in the coordinate diagram, and make two straight lines upward to intersect with the speed line. The area of the enclosed figure is the displacement size. The rectangle is enclosed at a constant speed; the triangle or trapezoid is used to encircle the city with constant speed, and the irregular figure with variable acceleration is enclosed
The relationship between displacement and area enclosed by velocity time image of high school physics
If the x-axis represents time, the y-axis represents the velocity, and the area represents the displacement
Why is velocity the ratio of displacement to time? Why not velocity to time,
Velocity: the displacement ratio, time velocity is vector, has size and direction, +, - represents direction
Speed: distance vs. time
Speed is a scalar, it only describes the speed of the object, not the direction of the object
In junior high school, we often regard speed as speed, while in high school we should distinguish speed and speed
RELATED INFORMATIONS
- 1. Find the S-T, V-T images of the intermediate velocity and the intermediate displacement velocity
- 2. What do acceleration and time images show Speed and time indicate acceleration. Distance and time are speed. What about acceleration and time?
- 3. The relationship between physical problems (displacement of uniform linear motion) and velocity The speed of a car before braking is 90 km / h, and the acceleration obtained by braking is 10 m / S 2 (1) The sliding distance within 10s after the start of braking Thank you very much!
- 4. It is proved that the instantaneous velocity at the midpoint of displacement is VX / 2 = √ VO2 + vt2 / 2 in the linear motion with uniform speed change
- 5. For an object moving in a straight line with uniform speed change, the instantaneous velocity at the intermediate moment and the instantaneous velocity at the intermediate displacement are calculated
- 6. When a body moves in free fall, the average velocity in a certain displacement is equal to half of the sum of the initial velocity and the final velocity,
- 7. Is velocity and velocity a ratio of displacement to time and a ratio of distance to time
- 8. Vehicle a and vehicle B pass the same displacement along the straight road. Vehicle a moves at the speed of 40 km / h in the first half of displacement and 60 km / h in the second half of displacement; vehicle B moves at the speed of 40 km / h and 60 km / h in the second half of the displacement （ ） A. . V A= . V b B. . V a ＞ . V b C. . V a ＜ . V b D. Can't be sure
- 9. Is the average velocity equal to the instantaneous velocity in any period of time of uniform linear motion? Is that correct? There is another question—— Is the displacement equal to the distance in any time of uniform linear motion? Is that correct?
- 10. Why can only represent two directions of an object's motion in the velocity and time image of uniformly variable speed linear motion? Can't the velocity be expressed in multiple directions
- 11. In the RT triangle ABC, ∠ C = 90 ° C = 34. If a to B is equal to 8 to 15, then a = b =
- 12. Given that the triangle ABC, P is a point in the triangle, through P as PD vertical BC, PE vertical AC, PF vertical AB, the height of triangle ABC h, it is proved that PD + PE + pf = H
- 13. In the triangle ABC, the angle c = 90 degrees, AC = BC, P is any point of AB, PE is vertical BC, PF is vertical AC, M is the midpoint of AB, connecting me, MF It is proved that me = MF
- 14. (Mathematics) in RT △ ABC, ∠ B = 90 degrees, BC > AB, BP = ba, BP=BA,BD⊥AC,PE⊥AC In the four line segments ad, BD, De, PE, there is a certain quantitative relationship between some line segments. Please write an equation to express the quantitative relationship (the equation contains 2 or 3 line segments), and explain the reasons for the equation
- 15. As shown in the figure, AB / / CD, ad vertical DC, ab = BC, and AE vertical BC 1. Prove that ad = AE If ad = 8, DC = 4, the length of AB is 4
- 16. As shown in the figure, we know ∠ 1 + ∠ 2 = 180 ° and ∠ 3 = ∠ B. try to judge the size relationship between ∠ AED and ∠ C, and rationalize the conclusion
- 17. As shown in the figure, in △ ABC, ∠ ABC = ∠ C = 2 ∠ a, BD ⊥ AC intersects AC at point D, then ∠ DBC=______ .
- 18. As shown in the figure, in △ ABC, D is a point on the edge of BC, ∠ 1 = ∠ 2, ∠ 3 = ∠ 4, ∠ BAC = 63 ° to find the degree of angle DAC
- 19. The lines AB and CD intersect at o.oe and of are bisectors of angle AOC and angle BOD respectively. (1) draw the figure. (2) ray OE The lines AB and CD intersect at points o.oe and of are bisectors of angle AOC and angle BOD respectively. (1) draw this figure. (2) are ray OE and of on the same line? (3) draw bisector of angle AOD OG.OE What is the location relationship with og?
- 20. As shown in the figure, the straight lines a and B are cut by the lines C and D, ∠ 1 and ∠ 2 are complementary angles to each other, ∠ 3 = 117 ° and the degree of ∠ 4 is calculated