10分 physics 快~

2007-10-16 3:28 am

A car in town X travels 120 km at N60E to town Y and then 50km at N30W to town Z.
(a) What is the total distance travelled by the car?
(b) If the car travels constantly at 60km h^-1, what is its average velocity?

回答 (1)

Audrey Hepburn

2007-10-16 3:36 am

✔ 最佳答案

a. Total distance

= 120 + 50

= 170 km

b. Time required to travel from town X to town Y

= Distance / speed

= 120 / 60

= 2 h

Time required to travel from town Y to town Z

= Distance / speed

= 50 / 60

= 0.833 h

= 50 mins

The three towns forms a right-angled triangle

So, by pythragus theorem,

Total displacement

= (120^2 + 50^2)^1/2

= 130 km

Total time required to travel

= 2 + 0.833

= 2.833 h

So, average velocity

= displacement / time

= 130 / 2.833

= 45.9 kmh^-1

= 45.9 X 1000 / 3600

= 12.7 ms^-1

參考: Myself~~~

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