Assam
Lv 6
Assam asked in 科學其他:科學 · 9 years ago

高中物理 力學問題

麻煩幫解一下 3QQ

1.在光滑平面上,將質量為5公斤與20公斤的物體,各施以水平定力F自靜止推行20公尺,若5公斤的物體費時5秒,則20公斤的物體需費時多少秒?

ANS:10秒

2.在水平面上,以10牛頓之水平推力將質量為3公斤的物體自靜止推行4公尺後,此物體之速率成為4公尺/秒,此物體所受之摩擦力為多少牛頓?

ANS:4牛頓

3.一油壓機其大小活塞直徑為40cm與5cm,今需舉起6400kg重之汽車,則小活塞至少需施力多少kg重?

ANS:100

4.設鋁與鐵之密度分別為2.7g/cm^3及7.8g/cm^3 ,以同為1000g重的實心鋁球與實心鐵球放入水中,則所受之浮力何者較大?

ANS:鋁球

5.要使一塊體積為2立方公尺的保麗龍完全沉入水中,則需在其上方施加多少牛頓的力?(保麗龍密度200kg/m^3 水密度1000kg/m^3 重力加速度10m/s^2)

ANS:16000

6.因摩擦力作用,質量為3公斤的物體在水平面上滑行9公尺後, 其速率為10公尺/秒變為8公尺/秒;則此物體的速率由8公尺/秒再降至4公尺/秒期間,將滑行若干公尺?

ANS:12

7.汽車以40公里/小時的車速運動,經緊急煞車滑行10公尺後靜止:設其為等加速直線運動,若此汽車以80公里/小時的車速運動,則在緊急煞車後汽車將

滑行若干公尺才會靜止?

ANS:40

1 Answer

Rating
  • 9 years ago
    Favorite Answer

    1.

    S=1/2(a)(t^2) --> 20=1/2(a)(5^2) --> a = 8/5 (m/s^2)

    F=ma --> F = (5)(8/5) = 8 N (the external force applied to 5kg))

    now apply the same external force to 20kg.

    F=ma --> 8=(20)(a) --> a= 2/5 (m/s^2)

    S=1/2(a)(t^2) --> 20 = 1/2(2/5)t^2 --> t= 10 sec

    2.

    v^2=2as--> 4^2=2(a)(4) --> a = 2 m/s^2

    F - f (frictional force) = ma --> 10 - f = 3 (2) --> f = 4N

    3.

    (area A) / (area B) = (force A) / (force B)

    (40^2) / (5^2) = (6400x9.8) / (Mx9.8) --> M = 100 kg

    4.

    because Aluminum has bigger volume !

    volume = mass / density

    5.

    F - f (floating force) + mg = 0 --> F - (2)(1000)(10) + (2)(200)(10) = 0

    --> F = 16000 N

    6.

    (V1)^2 =(V0)^2 + 2as --> 8^2 = 10^2 + 2(a)(10) --> a = 2 m/s^2

    (V2)^2 = (V1)^2 +2as --> 4^2 = 8^2 + 2(2)(s) --> s= 12 m

    7.

    40 km/hr = (40000)/(3600) m/s, 80 km/hr = (80000)/(3600)

    (V1)^2 = (V0)^2 +2as --> 0 = (40000)^2/(3600)^2 + 2(a)(10)

    --> a = - (40000)^2/[(2)(10)(3600)^2]

    (V1)^2 =(V0)^2 +2as

    --> 0 = (80000)^2/(3600)^2 + 2{- (40000)^2/[(2)(10)(3600)^2]}(s)

    --> s = 40 m

    Source(s): self
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