In construction site,a pile driver is used to drive a pile into the soil. It is released
from rest at time t=0.Fig.b(net force against time graph) shows how the net force F on the pile driver varies with t.Take upward as positive.Ignore air resistance.
(The graph:t=0s-3s, F=-30000N.t=3s-4s,F=100 000.After 4s,F=-30000.)
a)find the mass of the pile driver.
b)show that the momentum of the pile friver just before the impact is
-90 000 kg m s^-1.
c)find the momentum of the pile driver just after the impact.
F.4 Phy (Momentum)急..3q
2014-02-28 4:37 am
回答 (2)
2014-02-28 7:19 am
✔ 最佳答案
(a) During t = 0 to 3 s, the pile is under free fall and hence is acted by its own weight.That is, weight of pile driver = 30 000 N
mass of pile driver = 30 000/g kg = 3 000 kg
(tkae g, the acceleration due to gravity , equals to 10 m/s^2)
(b) Velocity of pile driver before impact = -g x 3 ( because v = u + at, with u = 0 m/s)
hence, velocity = -3g = -30 m/s
Momentum of pile driver = 3000 x (-30) kg.m/s = -90 000 kg.m/s
(v) Use: impulse = change of momentum
i.e. 100 000 x 1 = final momentum - initial momentum
100000 = final momentum - (-90000)
hence, final momentum = (100 000 - 90 000) kg.m/s = 10 000 kg.m/s
2014-02-28 7:10 am
Question a:
mg=-30000
m(-9.81)=-30000
m=3060 kg
Question b:
The required momentum
= Ft
= (-30000)(3)
= -90000 kg ms^-1
Question c:
The required momentum
= Ft
= (100000)(4-3)
= 100000 kg ms^-1
Please tell me if there is any mistake and you better show us the figure =.=''
mg=-30000
m(-9.81)=-30000
m=3060 kg
Question b:
The required momentum
= Ft
= (-30000)(3)
= -90000 kg ms^-1
Question c:
The required momentum
= Ft
= (100000)(4-3)
= 100000 kg ms^-1
Please tell me if there is any mistake and you better show us the figure =.=''
參考: Self-experience
收錄日期: 2021-04-20 14:57:53
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