AL physics─dynamics

2006-10-30 10:39 pm

A pendulum bob hangs from the roof of a train. If the train accelerates uniformly at 0.5m/s^2, what is the angle of inclination of the string of the pendulum from the vertical?

A. 0 degree
B. 3 degree
C. 10 degree
D. 30 degree

The anwser is B. I have no idea on solving the problem at all. please help me with clear steps.

回答 (1)

用戶120271

2006-10-31 2:42 am

✔ 最佳答案

If you draw a free body diagram, indicating all the given information, you should be able to get:

let T=tension of the string and the angle be x

since the movement has nothing to do with the y-axis, we can state that:

F(net) of y=Tcos x - mg=0 ------------------(1)

F(net) of x=Tsinx = 1/2 *m (F=ma) ----------------(2)

Since we do not want m, we can eliminate it by substitution:

Tcos x - mg =0

=> m= Tcos x /g ---------------(3)

Substitue (3) into (2),

Tsin x= 1/2 * Tcos x /g

taking g as 10m/s^2,

=> Tsin x=Tcos x /20

=> sin x / cos x =1/20

=> tan x = 1/20

=> x = (arc) tan 1/20

=> x = 3

Therefore the angle is 3 degrees

2006-10-30 18:43:35 補充：
The direction of the train is -----

2006-10-30 18:44:15 補充：
to the right

2006-10-30 18:44:46 補充：
>>>>>

👍 0 👎 0