Two 4:0-kg blocks are tied tog

[匿名]

2009-12-27 2:18 am

Two 4.0-kg blocks are tied together with a compressed spring between them. They are thrown from the ground with an initial velocity of 35m/s, 45度 above the horizontal. At the highest point of the trajectory they become untied and spring apart. About how far below the highest point is the center of mass of the two-block system 2.0 s later, before either fragment has hit the ground?
A. 12m
B. 20m
C. 31m
D. Can&#039;t tell because the velocities of the fragments are not given.
E. Can&#039;t tell because the coordinates of the highest point are not given.
ans: B

回答 (1)

Prof. Physics

2009-12-27 2:59 am

✔ 最佳答案

This is a rather tricky question.

At the highest point, when the spring is untied, it involves an internal force only.

So, for the centre of mass, there is no net external horizontal force acting on it, and it will travel in the original projectile trajectory.

That is to say, We just need a simple equation of motion to tackle it.

By s = ut + 1/2 at^2

s = 0 + 1/2 (10)(2)^2

s = 20 m

參考: Physics king

👍 1 👎 0