# Questions on Acceleration

by Raza
Tags: acceleration
 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.
Mentor
P: 40,689
 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.
 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?
Mentor
P: 40,689

## 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.
 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?
Mentor
P: 40,689
 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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