Question

妍

請問第一題(為什麼那兩個解法求的是最短時距🙏🏻

經典例題8*
B.D 2.
(A)cose
=
=-
則一物由靜止起沿AB下滑所須之時間為沿CD下滑時間之
半,設AB、AD及CD表面均光滑,則[多選]
自由弦圖
1. 一斜面在地面之投影大小恆為d,一物自此光滑斜面頂自由滑下,若欲使下滑時距
最短,則斜角應為
(A)30°
(B)37°
(C)45°
(D)53°
2. 如圖,一鉛直而立的圓O,AB、CD均表直徑,夾角為日,
(E)60°
A
C
2
D
((B)cose:
1
4
(C)若物體沿 AD 下滑需時,沿AB下滑需時2,則q: 右=1:2
(D)承(C)方式,但q:q =1:1
(E)承(C)方式,但:2=2:1
B
【解】:
Vo-D
10=45° 55. tmin=2√
=ggine/
2014202=180° l=d
a
gsing
Cose
•sing + Coso
28 = 180°-282
2
sin (20) = sin (180-202)=sin(202) B
01+02=95°
d
4₁ =
gsin (201)
V
testoste
P
30°
2
160°
A
2d
=2
d
zd
grind.coso √gisin (20) J
= √sing. Cost = sind cos
Sine.cosd≤2.等號成立條件→sin²e=cosg
e
70=45°
Self
sin(20)=2sing.Cose
sind. Wood = ± sin (20)
→ 9=45°
to 20k
too = 2 = 2(2Rase) = LAB (5% ))
acoso