physics is frustrating?

Question

So...I don't know how to do physics stuff. I don't even know what equations and what not I'm supposed to be using. But I figure if I can actually see a problem solved, I'll be able to figure out how these things are done.

A truck driver going 100 km/h applies the brakes, giving the truck a uniform decceleration of 6.50 m/s2 while it travels 20.0 m. (a.) what is the velocity of the truck in km/h at the end of this distance? (b.) how much time has elapsed?

Hey people...I'm not whining here, okay?! I have like 20 other problems to do, I just wanted one example! So...thank you all for your help.

Answer 1

Always list what is given first. In this example:

Vo = 100 km/h
a = - 6.50 m/s²
x = 20.0m

If you notice, your 100km/h doesn't match up with the other units, so we need to get that in m/s. You will find that he is going 27.78 m/s.

Now that your known variables, try to find an equation that uses them, and leaves 1 unknown. For this problem I would use the No name equation.

a. Vf² = Vo² + 2ax
You know everything except for Vf, so this is a good equation to use.
Vf = sqrt( (27.78m/s)² + 2(-6.50m/s²)(20.0m)
Vf = 22.62m/s or
81.43 km/h

Now that you have Vf you can find time (you could of found time first, but that involves the quadratic formula)

b. Vf = Vo + at
(Vf- Vo)/a = t
(22.62m/s - 27.78 m/s)/ (-6.5m/s²) = t
t = .794s

Don't know if you need sig figs or not.

Answer 2

The first thing you have to do is change 100km/h into m/sec so that all units are the same. You then use the formulas v = u + at and s = ut + 0.5a(t^2) where u is intial velocity,v is final velocity, t is time, a is acceleration rate (remembering that in this case it is negative). You know s, u and a so you can calculate t, from the second formula and then the final velocity from the first formula.. Im sorry but I'm not prepared to just do it for you. (Strange that the two parts of the question are this way round since you have to solve them the other way round.)

Answer 3

Yes, I know what you're saying. Back in high school I used to thoroughly neglect mechanics, vibrations,electricity, and so on.

I had math anxiety back then, so I would avoid those mathproblems.
Later I've figured that I just had a silly problem and that that material was not so tough after all.

But you'd really have to be interested in science, and then Science can be fun.

Sorry, I can't calculate this question for you. Though it is one of the basics of mechanics that you could solve by just applying the proper formula in your textbook.

Good luck.

Answer 4

Stop whining it's not that bad.

So the truck is going 100 km/h

Let's make this simple and convert this to m/sec

100 km/h * 1000m/1km * 1hr/60min * 1 min/60sec= 27.78 m/sec

Are you with me?

So the trucker is going to decelerate for some unknown time tending. And we don't know it right now.

So his start velocity is 100km/h; t = 0

Vf = Vo - a * t

So his ending velocity:

Vf = 27.78 - 6.5*tending


You know that distance = rate * time


We know his starting velocity and we have expressed his final velocity. And we know how long he traveled.

Now think of this.

Distance = (average speed) * time

what is his average speed?

His average speed is his starting speed plus his final speed divided by two. And we know the time he traveled

average speed = (Vo + Vf) /2

average speed = (27.78 + 27.78 - 6.5*tending)/2

We know he traveled at tending sec correct?

d = average speed * time

20 = (27.78 + 27.78 - 6.5*tending)/2 * tending

Now solve for t. This is a quadratic equation and the value of t has to be positive.

Can you handle it? Message with questions...Good Luck

Answer 5

yeah, physics can be tough. I won't do your homework for you, but I will give you this advice

When I had trouble in high school with physics, i called up a nearby college and spoke to the physics department and found a professor to tutor me cheap - like 20 bucks / hour

it really helped