第一题，有两向量（vectors)， vector A和 vector B ，vectorA 的大小为3.09，vector B的大小为3.06.这两个vectors 相乘的结果为 AxB(这是向量，所以A和B上都有一个箭头）= -5.10 k + 2.01 i 请问这两个向量的夹角为多少度

晕，来个人啊，怎地如此冷漠？

叉乘吗？注意这个等式成立 |a×b|=|a||b|sinθ

Consider a particle with initial velocity that has magnitude 12.0 and is directed 60.0 above the negative x axis.
Part A
What is the x component of ?

Consider a particle with initial velocity v that has magnitude 12.0 m/s and is directed 60.0° above the negative x axis.Part AWhat is the x component v(x) of v?

In a relay race, each contestant runs a distance 25.5m while carrying an egg balanced on a spoon, turns around, and comes back to the starting point. Jenny runs the first distance 25.5m in a time t = 20.4s . On the return trip she is more confident and takes only time = 14.9s .
What is her average velocity for the entire round trip?

A 7400kg rocket blasts off vertically from the launch pad with a constant upward acceleration of 2.35m/s^2 and feels no appreciable air resistance. When it has reached a height of 600m , its engines suddenly fail so that the only force acting on it is now gravity.
What is the maximum height this rocket will reach above the launch pad?
How much time after engine failure will elapse before the rocket comes crashing down to the launch pad?
How fast will it be moving just before it crashes?

这干嘛呢？竞赛么

A car and a truck start from rest at the same instant, with the car initially at some distance behind the truck. The truck has a constant acceleration of 2.18m/s^2, and the car an acceleration of 3.32m/s^2 . The car overtakes the truck after the truck has moved a distance 38.0m .
How much time does it take the car to overtake the truck?
How far was the car behind the truck initially?
What is the speed of the truck when they are abreast?
What is the speed of the car when they are abreast?
求推理式子+答案

Spiderman steps from the top of a tall building. He falls freely from rest to the ground a distance of h. He falls a distance of h/4 in the last interval of time of 1.2s of his fall.
What is the height h of the building?
这题牛逼，求高度

你应该找英语帝。。。。。。题都很简单，就是我翻译起来有点困难。。。

求答求答

A car comes to a bridge during a storm and finds the bridge washed out. The driver must get to the other side, so he decides to try leaping it with his car. The side the car is on is 18.6m above the river, while the opposite side is a mere 1.8m above the river. The river itself is a raging torrent 56.0m wide.
How fast should the car be traveling just as it leaves the cliff in order just to clear the river and land safely on the opposite side?
What is the speed of the car just before it lands safely on the other side?求解

In U.S. football, after a touchdown the team has the opportunity to earn one more point by kicking the ball over the bar between the goal posts. The bar is 3.00 m above the ground, and the ball is kicked from ground level, 11.0 m horizontally from the bar
There is a minimum angle above the ground such that if the ball is launched below this angle, it can never clear the bar, no matter how fast it is kicked. What is this angle?
If the ball is kicked at 55.0° above the horizontal, what must its initial speed be if it to just clear the bar? Express your answer in m/s.
If the ball is kicked at 55.0° above the horizontal, what must its initial speed be if it to just clear the bar? Express your answer in km/h
求解