a)Estimate the speed of Mr.Hu just before he reaches the water surface .
b)What is the magnitude of the average force exerted on him by the water .
更新1:
請問有冇一個情況之下要加埋自身重量(即mg)?
更新2:
我唔明 (F-mg).s = (1/2)mv^2 點解-mg b)v^2-u^2=2(a+g)s 點解加g
average force
2008-06-07 8:33 pm
Mr.Hu of mass 58 kg steps off a 10 m high platform and dives into water . Hecomes to rest when he is 4 m below the water surface .
a)Estimate the speed of Mr.Hu just before he reaches the water surface .
b)What is the magnitude of the average force exerted on him by the water .
a)Estimate the speed of Mr.Hu just before he reaches the water surface .
b)What is the magnitude of the average force exerted on him by the water .
回答 (2)
2008-06-08 10:28 am
✔ 最佳答案
(a) Use conservation of energy(1/2)mv^2 = mgh
where m is tha mass of Hu (=58 kg)
v is the speed just before entering into water
g is the acceleration due to gravity
h is the height of fall(=10m)
(1/2)(58)v^2 = 58x10x10
v^2 = 200 (m/s)^2, thus v = 14.14 m/s
(b) Use (work done) = change of kinetic energy
i.e. (net force)x distance = change of kinetic energy
(F-mg).s = (1/2)mv^2
where s is the distance travelled into water
F is the force exerted by water
(F - 58x10)x4 = (1/2)(58)(14.14^2)
solve for F gives F = 2030 N
2008-06-08 6:33 pm
a)v^2-u^2=2gs,v=14.14ms-1
b)v^2-u^2=2(a+g)s
0-14.14^2=2(a+10)*4
a=-35ms-2
F=ma
F=58*-35
F=-2030N
所以the magnitude of the average force exerted on him by the water=2030N
b)v^2-u^2=2(a+g)s
0-14.14^2=2(a+10)*4
a=-35ms-2
F=ma
F=58*-35
F=-2030N
所以the magnitude of the average force exerted on him by the water=2030N
參考: own
收錄日期: 2021-04-25 23:14:45
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