mg= ๐ใ ใจใใใใๅใใคใใใฃใฆใใใใใๅ ้ใใพใใใใญ๏ผ
ๅใใคใใใฃใฆใใใจใใฏใ
็ฉไฝใฏ็ญ้้ๅใใใใฏใ้ๆญขใใพใใใญใ
ๅใใใชใใใฐ่ณชๅใใฆใใ ใใ
Physics
Senior High
mg= ๐ใจใชใใชใใฎใฏใชใใงใใใใ๏ผ
ใใใๆนๆใใฆใใ ใใ๏ผ๏ผใใญใใใใพใ๐
70 ้ๅๆน็จๅผโ ๅณใฏใจใฌใใผใฟใผใ
ไธๆใใใจใใฎv-tๅณใงใใใ
ใใฎใจใฌใใผใฟใผใซใฎใฃใฆใใ่ณช้
50kgใฎไบบใใใจใฌใใผใฟใผใฎๅ ้, ็ญ้,
ใใใณๆธ้ไธญใซ, ใใใใๅบใซๅใผใๅใฎ
ๅคงใใใฏไฝNใใใใ ใใ้ๅๅ ้ๅบฆใฎๅคง
ใใใ9.8m/s2 ใจใใใ
V
50kg [m/s]
980
4
2
0 2 4 6 8 10 12 14 16
tใsใ
ไพ้ก13
170
ใใใใใคใณใ
ไบบใซใฏใใใๅใฏ้ๅ mg ใNใ ใจๅบใๅใผใๅ็ดๆๅ N [N] ใฎ2ๅใงใใใฎ2ๅใฎๅๅใงๅ ้ใใ
ใใไบบใฎๅ ้ๅบฆใฏใจใฌใใผใฟใผใฎๅ ้ๅบฆใจๅใใง,v-tๅณใฎๅพใ(=ๅ ้ๅบฆ)ใใๆฑใใใใใไบบใซใค
ใใฆ้ๅๆน็จๅผใ็ซใฆใใฐ,Nใฎๅคใๆฑใใใใจใใงใใใ ไบบใๅบใซๅใผใๅใฏๅ็ดๆๅNใฎๅไฝ็จ
N' ใง, ๅคงใใใฏ็ญใใ้ๅใใงใใใ
่งฃ็ญ t=0~2.0s ้, 2.0~8.0s ้, 8.0~
16.0s ้ใฎไบบ (ใจใฌใใผใฟใผ) ใฎๅ ้ๅบฆ
ใใใใใ a1,a2, as [m/s2], ๅบใไบบใซ
ๅใผใๅ็ดๆๅใฎๅคงใใใใใใใ N1,
N2, N3 [N] ใจใใใ ไบบใๅบใซๅใผใๅ
ใฏๅ็ดๆๅใฎๅไฝ็จ N1', N2', N3' [N]
ใงใใใ
้็ดๆนๅไธๅใใๆญฃใฎๅใใจใใฆ, ไบบ
ใซใคใใฆ้ๅๆน็จๅผใ็ซใฆใใ
ๅๅบ้ใซๅ
ฑ้ใซ
ma=N-mg ใใฃใฆ
N=m(g+ฮฑ) [N]
8.0-04.0m/s2
aโ=
t=0~2.0s ้
2.0-0
ใใฃใฆ, โ ๅผใใ N' = N=50ร(9.8+4.0) = 6.9ร102N
t=2.0~8.0s ้ a2 = 0m/sยฒ
โ ๅผใใ N2' = N2=50ร(9.8+0)=4.9ร102N
0-8.0
16.0 -8.0
โ ๅผใใ Ng'โฒ = N=50ร(9.8-1.0)=4.4ร10ยฐN
ไบบใซใฏใใใๅ
t=8.0 ~ 16.0s ้ฮฑ3=
=-1.0m/s2
LEVE
F
N'
ใจใฌใใผใฟใผใซ
ใฏใใใๅ
็ฌฌ4็ซ โ ้ๅใฎๆณๅ 33
......1
1 ใจใฌใใผใฟใผๅ
ใงไฝ้
่จใซใฎใฃใๅ ดๅใฏ,่ณช้1
kgใฎ็ฉไฝใฎ้ใใ
mg=1xg=g=9.8N ใงใใ
ใใใ ไฝ้่จใฎ้ใฎใใ็ฎ็
ใใฏใใใใๆฌกใฎใใใซใชใใ
50ร(9.8+4.0)
N'':
-โ70kg
9.8
N2โฒ:
BAT
50ร(9.8+0)
9.8
=50kg
50ร(9.8-1.0)
9.8
N3':
-โ45kg
็ญ้ใฎๅ ดๅ (N2') ใฎๅคใฏ,้
ๆญขใฎๅ ดๅใจๅใใงใใใ
Answers
ใใใใ้ๅใ่ฆณๆธฌใใ่ฆ็นใใใกใใใกใใซใชใฃใฆใใๆฐใใใพใใใจใฌใใผใฟใผใฎๅคใใ่ฆใ่ฆ็นใง่ใใฆใฟใพใใใใไบบใซๅใๅใ่ใใใจๅบใใใฎๅ็ดๆๅใจ้ๅใๅใใฆใใพใใใใพไบบใฎๅ ้ๅบฆใฏใจใฌใใผใฟใผใจ็ญใใaใจใชใใฎใง้ๅๆน็จๅผใใma=mg-Nใจใใๅผใๅพใใใพใใ
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