PHYSICS GURUS...NEED HELP!!

[j2legend]

I have a problem.

How long would it take for a car going 90km/hr to slow down (decelerate) to 60km/hr in 50 yards?
Is this enough information to solve the problem without any other variables or information?

My guess is no because I can't solve it. But maybe I'm not going about this correctly.

 

[j2legend]

I have a problem.

How long would it take for a car going 90km/hr to slow down (decelerate) to 60km/hr in 50 yards?
Is this enough information to solve the problem without any other variables or information?

My guess is no because I can't solve it. But maybe I'm not going about this correctly.

 

[wearinthefourfive]

You'd need the forces acting against the car in order to solve it (friction and such).

 

[wearinthefourfive]

You'd need the forces acting against the car in order to solve it (friction and such).

 

[th3ownly]

i think you just use the equation

s=(1/2)*(v+u)*t

s=distance
v=final velocity
u=initial velocity
solve for t

 

[th3ownly]

i think you just use the equation

s=(1/2)*(v+u)*t

s=distance
v=final velocity
u=initial velocity
solve for t

 

[th3ownly]

and honestly dude i just went to http://en.wikipedia.org/wiki/Equations_of_motion

and looked for the equation that had your knowns and the unknown

 

[th3ownly]

and honestly dude i just went to http://en.wikipedia.org/wiki/Equations_of_motion

and looked for the equation that had your knowns and the unknown

 

[dt43]

d = 1/2(v + v0) * t

this is one of the elementary kinematics equations. you will fail hard if you don't know all of those by heart.

 

[dt43]

d = 1/2(v + v0) * t

this is one of the elementary kinematics equations. you will fail hard if you don't know all of those by heart.

 

[j2legend]

OMG, I can't believe I missed that.
It's been awhile since I was in school for physics.
I'm actually fighting my way out of a speeding ticket.

 

[j2legend]

OMG, I can't believe I missed that.
It's been awhile since I was in school for physics.
I'm actually fighting my way out of a speeding ticket.

 

[jking0821]

Since when did NT become a HW help forum.



We become more versatile every day.

 

[jking0821]

Since when did NT become a HW help forum.



We become more versatile every day.

 

[turboman]

Originally Posted by J2Legend

I have a problem.

How long would it take for a car going 90km/hr to slow down (decelerate) to 60km/hr in 50 yards?
Is this enough information to solve the problem without any other variables or information?

My guess is no because I can't solve it. But maybe I'm not going about this correctly.

Convert 50 yards to meters. 45.72 meters. Convert speeds to m/s. 90km/h = 25 m/s. 60km/h = 16.7 m/s

Spoiler

Spoiler

Spoiler [+]

Spoiler

Vf ^2 = Vo^2 + 2A(X)
VelocityFinal squared = VelocityOriginal squared + 2(Rate of Deceleration)(Distance traveled)
Here you solve for the rate of deceleration
(16.67 m/s)^2 = (25 m/s)^2 + 2(A)(45.72m)
a = 3.796 m/s/s

Solve for time:
Vf = Vo + at
VelocityFinal = VelocityOriginal + (Acceleration * Time)
25 m/s = 16.67 m/s + (3.796)t
8.333m/s = 3.796m/s/s * t

Final answer:
t = 2.1952 seconds

Mind the units always. Someone please try to find an answer too. I've been out of physics for awhile. Might be wrong. Just my attempt.

 

[turboman]

Originally Posted by J2Legend

I have a problem.

How long would it take for a car going 90km/hr to slow down (decelerate) to 60km/hr in 50 yards?
Is this enough information to solve the problem without any other variables or information?

My guess is no because I can't solve it. But maybe I'm not going about this correctly.

Convert 50 yards to meters. 45.72 meters. Convert speeds to m/s. 90km/h = 25 m/s. 60km/h = 16.7 m/s

Spoiler

Spoiler

Spoiler [+]

Spoiler

Vf ^2 = Vo^2 + 2A(X)
VelocityFinal squared = VelocityOriginal squared + 2(Rate of Deceleration)(Distance traveled)
Here you solve for the rate of deceleration
(16.67 m/s)^2 = (25 m/s)^2 + 2(A)(45.72m)
a = 3.796 m/s/s

Solve for time:
Vf = Vo + at
VelocityFinal = VelocityOriginal + (Acceleration * Time)
25 m/s = 16.67 m/s + (3.796)t
8.333m/s = 3.796m/s/s * t

Final answer:
t = 2.1952 seconds

Mind the units always. Someone please try to find an answer too. I've been out of physics for awhile. Might be wrong. Just my attempt.

 

[proper english]

you got pulled over, didnt you OP?  im using this same exact formula for my Trial By Deceleration.

 

[proper english]

you got pulled over, didnt you OP?  im using this same exact formula for my Trial By Deceleration.

 

[j2legend]

^^ A friend of mine did.

Personally 11 over the limit is no big deal, but oh well

 

[j2legend]

^^ A friend of mine did.

Personally 11 over the limit is no big deal, but oh well

 

[j2legend]

^^ A friend of mine did.

Personally 11 over the limit is no big deal, but oh well

 

[j2legend]

^^ A friend of mine did.

Personally 11 over the limit is no big deal, but oh well

 

[proper english]

since were on this subject.. can someone help me out with this.. got pulled over the other day. Officer clocked me on the radar gun going 52mph from a complete stop within a quarter mile length..  what am i missing here? 

BTW, i drive an IS300.. looked up quarter mile times for it: 15.2secs..  

someone told me to divide the MPH (52) by the length (.25 miles).. what i got was: .00480... 4seconds? 

idk #$%^ about math, if you can already tell. 

 

[proper english]

since were on this subject.. can someone help me out with this.. got pulled over the other day. Officer clocked me on the radar gun going 52mph from a complete stop within a quarter mile length..  what am i missing here? 

BTW, i drive an IS300.. looked up quarter mile times for it: 15.2secs..  

someone told me to divide the MPH (52) by the length (.25 miles).. what i got was: .00480... 4seconds? 

idk #$%^ about math, if you can already tell. 

 

[okaykk]

Originally Posted by proper english

since were on this subject.. can someone help me out with this.. got pulled over the other day. Officer clocked me on the radar gun going 52mph from a complete stop within a quarter mile length..  what am i missing here? 

BTW, i drive an IS300.. looked up quarter mile times for it: 15.2secs..  

someone told me to divide the MPH (52) by the length (.25 miles).. what i got was: .00480... 4seconds? 

idk #$%^ about math, if you can already tell. 

Do you have a speeding ticket or an excessive acceleration or both?