A car going 70 mph stops in 145 feet. Find the acceleration, assuming it is constant. Give your answer in feet per second-squared.

Question

osanseviero · Answer

You should post this in the physics group.

anonymous · Answer

Yet, this is from my math class. This teacher gives me brain cramps.

amistre64 · Answer

acceleration is defined as change in velocity over time

so (vf - vi)/time

amistre64 · Answer

hmm

v = dt

t = d/v;   ft/(ft/sec) = sec  so the dimensions work fine

amistre64 · Answer

gonna have to convert miles/hr to feet/sec prolly .. or vice versa

amistre64 · Answer

get my mind right

velocity is a measure of miles /hour

v = d/t

therefore   t = d/v  had it right in my head

amistre64 · Answer

we can work it backwards too,  start at 0 and speed up to 70mph over 145 feet .... 

a = k

v = kt + c , v(0) = 0, c=0  
      kt = 70mph, when t=70mph/k

d = 1/2 kt^2 + j, d(0) = 0 so j=0

d(70mph/k) = 145feet

145ft = 1/2 k(70mph/k)^2 

290ft = (70mph)^2/k

k =  (70mph)^2/290ft

amistre64 · Answer

convert as needed :)