運動力學 20分 torque and angular

2015-05-04 4:32 am

Question picture
Torque
http://upload.lsforum.net/users/public/b424061v176.png
http://upload.lsforum.net/users/public/h77662n176.png
How to do?

angular
http://upload.lsforum.net/users/public/j210433v176.png
a.
20=0.7x angular velocity
angular velocity= 28.6 rad/s

b.
average angular acceleration=28.6/0.4
average angular acceleration=71.4rad/s/s

c.
average tangential acceleration=0.7x71.4
average tangential acceleration=50m/s/s

d.
average radial acceleration= 0.7x28.6^2
average radial acceleration=572.6m/s/s

e. how to do?

更新1:

1.(a) (ii) Torque = 35 x 0.3sin(45) N.m = 7.425 N.m Sin 45 點來?可唔可以畫幅圖來?

回答 (1)

天同

2015-05-04 7:59 pm

✔ 最佳答案

1.(a)(i) Torque = 35 x 0.3.sin(0) N.m = 0 N.m
(ii) Torque = 35 x 0.3sin(45) N.m = 7.425 N.m
(iii) Torque = 35 x 0.3sin(90) N.m = 10.5 N.m

(b) Let F be the medial deltoid force
At position B: [F.sin(15)] x 0.05 = 7.425
i.e. F = 574 N

At position C: [F.sin(15)] x 0.05 = 10.5
i.e. F = 811 N

(c) The medial deltoid muscle needs to contract in order to give the necessary torque.

2.(e) Assume the pitch is completed in 0.4 s as before, the angular velocity will remains the same. Shortening the pitching arm will give a lower tangential speed of the ball at release.

2015-05-04 16:13:45 補充：
Q:Sin 45 點來?
A: The arm is lifted at 45 degress with the vertical. 0.3sin(45) is the perpendicular distance between the arm's weight and the shoulder joint.

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