Re: [問題]請問一題摩擦力
由摩擦力定義 f=μN 得:
f_1 = μ N_1 (1)
f_2 = 0.2 N_2 (2)
由 ΣF=0 得:
N_2 = f_1 (3)
N_1 + f_2 = 10 + 45 (4)
對B點取 Στ=0 得:
3 3√3 3 1
N_1 ×─ = f_1 ×── + 10 ×─ + 45 ×─ (5)
2 2 4 2
解聯立方程組(1)(2)(3)(4)(5)得結果:
μ ≒ 0.35
-------------
應該是這樣啦。。。
--
※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 1.165.123.37
※ 文章網址: https://www.ptt.cc/bbs/Physics/M.1485166395.A.674.html
推
01/23 19:23, , 1F
01/23 19:23, 1F
※ 編輯: ycldingo (1.165.123.37), 01/23/2017 20:29:05
→
01/23 22:58, , 2F
01/23 22:58, 2F
→
01/23 22:59, , 3F
01/23 22:59, 3F
→
01/23 22:59, , 4F
01/23 22:59, 4F
→
01/23 23:00, , 5F
01/23 23:00, 5F
1.
「梯開始下滑」 → 我的解讀為與地面洽達最大靜摩擦,同時
「梯與牆間摩擦係數0.2」 → 未指明為動摩擦係數或靜摩擦係數
根據 動摩擦發生於接觸面發生錯動 之情況與 「梯開始下滑」,故假設0.2為靜摩擦係數
2.
若其中一點摩擦力未達最大靜摩擦力 → 與接觸面不發生錯動
又樓梯為一體,故另一點應也未動
因此我假設兩者皆達最大靜摩擦
※ 編輯: ycldingo (1.165.123.37), 01/24/2017 00:06:35
→
01/24 01:01, , 6F
01/24 01:01, 6F
→
01/24 01:02, , 7F
01/24 01:02, 7F
→
01/24 01:02, , 8F
01/24 01:02, 8F
推
01/24 08:39, , 9F
01/24 08:39, 9F
→
01/24 08:39, , 10F
01/24 08:39, 10F
→
01/24 08:39, , 11F
01/24 08:39, 11F
看法同Y大
上面第2.點是我認為不會有一個超過一個未超過的原因
※ 編輯: ycldingo (1.165.123.37), 01/24/2017 09:26:58
→
01/24 13:02, , 12F
01/24 13:02, 12F
→
01/24 13:02, , 13F
01/24 13:02, 13F
→
01/24 13:03, , 14F
01/24 13:03, 14F
I.
若為牆壁光滑的case → 牆給梯的作用力只剩下正向力N_2
→ 方程組改為:
f_1 = μ N_1 (1)
f_1 = N_2 (3)
N_1 = 10 + 45 (4*)
3 3√3 3 1
N_1 ×─ = f_1 ×── + 10 ×─ + 45 ×─ (5)
2 2 4 2
這種情況下梯與地面的摩擦力為最大、梯與牆間無摩擦。此為yyc所言例子。
II.
但在牆與梯、地與梯間皆有摩擦力的情況下,兩邊的摩擦力種類為何?
已知:1. 最大靜摩擦力發生時,物體相對接觸面恰有錯動
2. 動摩擦力必有錯動
3. 此題條件:梯開始下滑(我解釋為恰開始滑動)
故:梯開始下滑 → 恰滑動
→ 最大靜摩擦
→ 題給摩擦係數為靜摩擦係數
III.
至於為什麼兩邊都是最大靜摩擦?我的認知如下:
梯的一端移動另一端必跟著移動(假設樓梯無分離),故一端恰移動 → 另端恰移動
→ 兩端皆最大靜摩擦
→
01/24 13:05, , 15F
01/24 13:05, 15F
→
01/24 13:06, , 16F
01/24 13:06, 16F
→
01/24 13:06, , 17F
01/24 13:06, 17F
推
01/24 13:18, , 18F
01/24 13:18, 18F
推
01/24 13:22, , 19F
01/24 13:22, 19F
推
01/24 17:08, , 20F
01/24 17:08, 20F
※ 編輯: ycldingo (1.165.123.37), 01/24/2017 17:34:15
→
01/28 02:01, , 21F
01/28 02:01, 21F
→
01/28 02:02, , 22F
01/28 02:02, 22F
→
01/28 02:02, , 23F
01/28 02:02, 23F
→
01/28 02:02, , 24F
01/28 02:02, 24F
→
01/28 11:56, , 25F
01/28 11:56, 25F
→
01/28 11:56, , 26F
01/28 11:56, 26F
→
01/28 11:57, , 27F
01/28 11:57, 27F
→
01/28 11:58, , 28F
01/28 11:58, 28F
→
01/28 12:00, , 29F
01/28 12:00, 29F
→
01/28 12:01, , 30F
01/28 12:01, 30F
→
01/28 12:01, , 31F
01/28 12:01, 31F
→
01/28 12:02, , 32F
01/28 12:02, 32F
→
01/28 12:03, , 33F
01/28 12:03, 33F
→
01/28 12:04, , 34F
01/28 12:04, 34F
→
01/28 12:05, , 35F
01/28 12:05, 35F
→
01/28 12:05, , 36F
01/28 12:05, 36F
推
01/28 21:31, , 37F
01/28 21:31, 37F
→
01/28 21:31, , 38F
01/28 21:31, 38F
→
01/29 00:19, , 39F
01/29 00:19, 39F
→
01/29 00:19, , 40F
01/29 00:19, 40F
→
01/29 00:44, , 41F
01/29 00:44, 41F
→
01/29 00:45, , 42F
01/29 00:45, 42F
→
01/29 00:45, , 43F
01/29 00:45, 43F
→
01/29 00:46, , 44F
01/29 00:46, 44F
→
01/29 01:01, , 45F
01/29 01:01, 45F
→
01/29 01:01, , 46F
01/29 01:01, 46F
→
01/29 01:03, , 47F
01/29 01:03, 47F
→
01/29 01:03, , 48F
01/29 01:03, 48F
→
01/29 01:05, , 49F
01/29 01:05, 49F
→
01/29 01:05, , 50F
01/29 01:05, 50F
→
01/29 01:06, , 51F
01/29 01:06, 51F
→
01/29 01:38, , 52F
01/29 01:38, 52F
→
01/29 01:38, , 53F
01/29 01:38, 53F
→
01/29 01:39, , 54F
01/29 01:39, 54F
→
01/29 01:40, , 55F
01/29 01:40, 55F
→
01/29 01:40, , 56F
01/29 01:40, 56F
→
01/29 01:41, , 57F
01/29 01:41, 57F
→
01/29 01:42, , 58F
01/29 01:42, 58F
→
01/29 01:42, , 59F
01/29 01:42, 59F
→
01/29 01:51, , 60F
01/29 01:51, 60F
→
01/29 01:51, , 61F
01/29 01:51, 61F
推
01/29 19:39, , 62F
01/29 19:39, 62F
→
01/29 19:39, , 63F
01/29 19:39, 63F
→
01/29 19:40, , 64F
01/29 19:40, 64F
→
01/30 00:18, , 65F
01/30 00:18, 65F
→
01/30 00:18, , 66F
01/30 00:18, 66F
→
01/30 00:20, , 67F
01/30 00:20, 67F
討論串 (同標題文章)