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If the acceleration direction of the vehicle is consistent with the speed direction, when the acceleration decreases, then () A. The speed of the car also decreases B. The speed of the car first decreases and then increases C. When the acceleration decreases to zero, the car comes to a standstill D. When the acceleration decreases to zero, the speed of the car reaches the maximum
A. B. the acceleration direction of the car is consistent with the speed direction, and the car is accelerating. Therefore, a and B are wrong
C. D. when the acceleration decreases, the speed of the car increases from fast to slow, but the speed is still increasing. When the acceleration is zero, the car moves at a uniform speed and the speed reaches the maximum. Therefore, C is wrong and D is correct
So choose D
When the acceleration decreases to zero, the speed of the car reaches the maximum?
"When the acceleration decreases to zero, the speed of the car reaches the maximum" is actually a wrong proposition. Acceleration can not be unilaterally understood as the acceleration when accelerating. This proposition makes such a mistake. Acceleration is a vector with direction, which is when it is the same as the moving direction of the object, and is negative when it is opposite. When the car accelerates, the acceleration is reduced to
The death acceleration is 500g (g = 10m / s), which means that if the driving speed exceeds this value, life will be in danger. Such a large acceleration can not be reached by ordinary vehicles, but it will reach this value in traffic accidents. Two motorcycles collide with each other at the speed of 36km / h, and the collision time is 2x (the negative third power of 10) s. will the driver's life be in danger? Note: do you need to add the speeds of the two vehicles? The teacher said it didn't need to be added!
It's to be added
The closing speed is v = 72 ÷ 3.6 = 20m / s
The acceleration is a = V / T = 20 / 0.002 = 10000m / S2, greater than 500g (5000m / S2)
So life is in danger
What your teacher said is wrong, or you heard the wrong meaning. Anyway, no matter what the reason is, it must be added. Think about it, if you don't add it, it's equivalent to that one motorcycle doesn't move and the other hits him?
A car originally travels at a constant speed, and then drives at an acceleration of 2 meters without quadratic second. Starting from the acceleration, it takes 12 seconds Driving for 264 meters; (1) What is the average speed of the car in 12 seconds? (2) What is the initial speed when the car begins to accelerate?
1）v=s/t v=22m/s
2)s=v0t+1/2at^2 264=12v0+12^2
v0=10m/s
What are the advantages and disadvantages of conjugate gradient method compared with Newton method
Newton method or damped Newton method has fast convergence speed, but the amount of calculation is too large to calculate the second-order partial derivative matrix and its inverse matrix;
The convergence speed of conjugate shaving method is much faster than that of steepest descent method, and the calculation of Hessian matrix is avoided;
Is the optimal solution obtained by gradient method and Newton method global optimal or local optimal
Are locally optimal
In fact, all iterative methods get only local optima
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