(1) The acceleration of the stone is constant.
(2) The total energy of the stone is conserved.
(3) The momentum of the stone is conserved.
更新1:
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Motion
2007-03-05 7:30 am
A stone is thrown vertically upwards and it finally falls back to the starting point. Assume air resistance is negligible. Which of the following statements is/are true throughout the motion ?
(1) The acceleration of the stone is constant.
(2) The total energy of the stone is conserved.
(3) The momentum of the stone is conserved.
(1) The acceleration of the stone is constant.
(2) The total energy of the stone is conserved.
(3) The momentum of the stone is conserved.
回答 (2)
2007-03-05 7:36 am
✔ 最佳答案
(1) True - always = -g(2) True - as PE + KE = constant and no loss due to air resistance
(3) not true - as external force of gravity is acting on it
2007-03-05 7:40 am
(1) True
air resistance is negligible, so the acceration is only due to the acce due to gratity.,pointing to the ground (9.81 m per s )
(2) True
When the stone move upwards KE turn to PE
At highest point , KE is 0 and PE max.
When falling dwn, PE turn back to KE.
(3)False
monentum =mass x velocity Since KE of the motion is changing thoughtout the jounrey , the vaiue of monentum varies .
Note if air resi is counted ,then the acc is decreasing thoughout ,
When moving up, ,
Air Resistance and g are in same dir ( Net a =g+r)
Highest pt (Net a=g)
When moving down
r and g are opposite dir , but g.>r
Net a =g-r
air resistance is negligible, so the acceration is only due to the acce due to gratity.,pointing to the ground (9.81 m per s )
(2) True
When the stone move upwards KE turn to PE
At highest point , KE is 0 and PE max.
When falling dwn, PE turn back to KE.
(3)False
monentum =mass x velocity Since KE of the motion is changing thoughtout the jounrey , the vaiue of monentum varies .
Note if air resi is counted ,then the acc is decreasing thoughout ,
When moving up, ,
Air Resistance and g are in same dir ( Net a =g+r)
Highest pt (Net a=g)
When moving down
r and g are opposite dir , but g.>r
Net a =g-r
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