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Questions on Acceleration

by Raza
Tags: acceleration
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Raza
#1
Nov7-06, 05:02 PM
P: 208
Okay, Can someone do these for me so I can understand acceleration:

My car can reach a maximum speed of 150km/hr. And my car can acclerate at 5km/hr2. How long will it take for my car to reach 150km/hr from rest.
I know acceleration is the velocity of the velocity and the eqn for acceleration but I don't know how it works.
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Doc Al
#2
Nov7-06, 06:27 PM
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Quote Quote by Raza
My car can reach a maximum speed of 150km/hr. And my car can acclerate at 5km/hr2. How long will it take for my car to reach 150km/hr from rest.
From the definition of acceleration as the rate of change of velocity, the average acceleration will equal the change in velocity divided by the time:
a = (Vf - Vi)/t or Vf = Vi + at

Plugging in your values and solving for time gives: t = 30 hr.
Raza
#3
Nov7-06, 06:35 PM
P: 208
So in 1 hour, it went from 0km/hr to 5km/hr. And in the 2nd, it went to 10km\hr. In 5 hours, how much distance did it cover?

Doc Al
#4
Nov7-06, 06:47 PM
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Questions on Acceleration

At the end of 5 hours, its speed will be 25 km/hr. During those 5 hours the average speed, since it started from rest, is 12.5 km/hr. Use that speed to calculate the distance: 62.5 km.
Raza
#5
Nov7-06, 06:58 PM
P: 208
1hr=5km/hr
2hr=10km/hr
3hr=15km/hr
4hr=20km/hr
5hr=25km/hr
5+10+15+20+25=75
75/5=15km\hr
at the end of 5hr, it will be 15km\hr x 5hr, which is 75km.
Why is the answer 62.5km?
Doc Al
#6
Nov7-06, 07:09 PM
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Quote Quote by Raza
1hr=5km/hr
2hr=10km/hr
3hr=15km/hr
4hr=20km/hr
5hr=25km/hr
These are the speeds at those times. So?
5+10+15+20+25=75
What's this supposed to represent? Not the distance travel in each hour, I hope.

If that's what you're doing, start by working out the distance traveled in the first hour. Hint: It's not 5 km.

(I'm going to split off this discussion into a separate thread in "Intro Phys".)


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