question: about energy

2007-05-29 11:03 pm

A cart with total mass 1200 kg runs down from rest at "H" to the terminal planform. "H" is 30 m above the terminal platform (vertically). Track provides friction of 300 N throughout the journey. The cart travels a distance of 150 m to reach the highest point "A" of the vertical loop, which 20 m above the terminal (vertically). In moving from H to A, what is: a) loss in potential energy; b) work done against friction; c) gain in kinetic energy of the cart

回答 (1)

用戶40379

2007-05-30 8:38 am

✔ 最佳答案

A cart with total mass 1200 kg runs down from rest at "H"; to the terminal planform. "H"; is 30 m above the terminal platform (vertically). Track provides friction of 300 N throughout the journey. The cart travels a distance of 150 m to reach the highest point "A"; of the vertical loop, which 20 m above the terminal (vertically). In moving from H to A, what is: a) loss in potential energy;
ΔPE = mgh = 1200 x 10 x (30 – 20)
= 120,000J

b) work done against friction;
Wf = f S = 300 x 150
= 45,000J

c) gain in kinetic energy of the cart
ΔKE =ΔPE – Wf = 120,000 – 45,000
= 75,000

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