In the ice ballet show,two skaters are sliding smoothly on ice with speed 15ms^-1.The man throws his parther forward at 28ms^-1.If the weight of the man and that of the woman are 75kg and 50kg respectively,what will be the kinetic energy supplied by the man?
A.1500J
B.1800J
C.7040J
D,14100J
When the golf ball of mass 40g is 5m away from the hole,it is given a sharp horizontal push from rest and just reaches the hole.Find the intital speed of the golf ball if the average resistive force exerted on the ball is 0.03N
A.2.74ms^-1
B.7.50ms^-1
C.8.94ms^-1
D.9.76ms^-1
phy MC
2010-02-21 11:31 pm
回答 (2)
2010-02-26 11:33 pm
無最佳解答
2010-02-22 12:23 am
1. Use conservation of momentum to find the speed of the man,
(75 + 50).(15) = 50 x 28 + 75v
where v is the speed of man after he has thrown out his partner
splve for v gives v = 6.33 m/s
Therfore, change in kinetic energy
= [(1/2)(75)(6.33)^2 + (1/2)(50)(28^2)] - (1/2)(75+28)(15^2) J
= 7040 J
2. Use work done = cahnge of kinetic energy
0.03 x 5 = (1/2)(40/1000)v^2
where v is the initial speed of the ball
solve for v gives v = 2.74 m/s
(75 + 50).(15) = 50 x 28 + 75v
where v is the speed of man after he has thrown out his partner
splve for v gives v = 6.33 m/s
Therfore, change in kinetic energy
= [(1/2)(75)(6.33)^2 + (1/2)(50)(28^2)] - (1/2)(75+28)(15^2) J
= 7040 J
2. Use work done = cahnge of kinetic energy
0.03 x 5 = (1/2)(40/1000)v^2
where v is the initial speed of the ball
solve for v gives v = 2.74 m/s
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