The fast and the curious

A "ten second car" is a car that can go 1/4 mile in 10 seconds starting from rest. What's the acceleration of such a ten second car in meters/second 2 \mbox{meters/second}^2 ?

Details and assumptions

  • Assume the acceleration is a constant.
  • There are 1.609 km in a mile.


The answer is 8.04.

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6 solutions

Abrar Nihar
Sep 2, 2013

If the initial velocity is v 0 v_0 , total distance traveled is d d , the taken time is t t and the acceleration is a a , then...

~

d = v 0 t + 1 2 a t 2 \Large{d=v_0 t+\frac {1}{2} at^2}

~

We have the values...

~

v 0 = 0 \large{v_0 = 0}

~

d = 1 4 miles \large{d=\frac {1}{4} \textrm{miles}}

= ( 1 4 × 1.609 × 1000 ) meters ~~~~\large{= (\frac {1}{4} \times 1.609 \times 1000) \textrm{meters}}

= 402.25 meters ~~~~\large{= 402.25 ~ \textrm{meters}}

~

t = 10 seconds \large{t=10 ~ \textrm{seconds}}

~

Plugging in the values, we get...

~

402.25 meters = 0 + 1 2 × a × ( 10 second ) 2 \large{402.25 ~ \textrm{meters}=0+\frac{1}{2}\times a \times (10~\textrm{second})^2}

a = \large{a=} 402.25 meters 50 second 2 \Large{\frac{402.25 ~ \textrm{meters}}{50 ~ \textrm{second}^2}}

a = 8.045 meter/second 2 \Large{\therefore a=8.045 ~ \textrm{meter/second}^2}

I, instead, used the formula a=(v f^2-v i^2)/2s. I then plugged in 1/4 mi for s, 40 for v f, 0 for v i, solved and put it into the right unit. But I got the wrong answer. Why was that?

Daniel Liu - 7 years, 9 months ago

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How did u put in 40 for v_f??? Where did u get that???

Abrar Nihar - 7 years, 9 months ago

Where did you get 50 second^2 ?

Aida Arissa - 7 years, 9 months ago

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402.25 meters = 0 + ( 1 2 × a × ( 10 second ) 2 ) 402.25~\textrm{meters}=0+(\frac{1}{2} \times a \times (10~\textrm{second})^2)

402.25 meters = a × 1 2 × 100 second 2 \Longrightarrow 402.25~\textrm{meters}=a \times \frac{1}{2} \times 100~\textrm{second}^2

402.25 meters = a × 50 second 2 \Longrightarrow 402.25~\textrm{meters}=a \times 50~\textrm{second}^2

402.25 meters 50 second 2 = a \Longrightarrow \frac{402.25~\textrm{meters}}{50~\textrm{second}^2}=a

a = 8.045 meter/second 2 \therefore a = 8.045~\textrm{meter/second}^2

Hope that helps! :)

Abrar Nihar - 7 years, 9 months ago
Chin Fong Wong
Sep 2, 2013

From s = u t + 1 2 a t 2 s=ut + \frac{1}{2}at^2 ,

where s = 1 4 m i l e = 1 4 ( 1.609 ) k m , u = 0 , a = ? , t = 10 s=\frac{1}{4}mile=\frac{1}{4}(1.609)km, u=0, a=?, t=10

substitute inside and we get 8.045 m / s 2 8.045m/s^2

I solved it using the kinematic equation too!

Joshua Crouch - 7 years, 9 months ago

but..... after putting values, answer was not found as yours..

Iram Udoy - 7 years, 9 months ago

Hello all,

Given that the s = 0.25 mile = 0.25 (1.609)(1000) = 402.25 m, u = 0 m/s,

By applying the formula,

s = ut + 0.5at^2

402.25 = 0(10) + (0.5)(a)(10)^2

50a = 402.25

a = 8.045 m/s/s...

thanks...

Eraz Ahmed
Sep 10, 2013

We know that, s=ut+(0.5)a*t^2 (here we assume u as the initial velocity , a as the accelaration and t is the time elapsed and s is the distance it has gone )

Now, the car was started from rest so u=0 and s=1/4mile =0.40225KM=402.25m and t=10s now , using the information on the formula we will get that ,

402.25=(0.5)a*t^2 =>a=8.045m/s^2

Parag Motwani
Sep 6, 2013

1/4 mile of a mile= 1/4*1609 meters =402.25 meters

u=0 a=? (not known) t=10 seconds s=402.25 meters

s=ut+1/2*at²

402.25= 0+1/2*a100

4.02=1/2*a

a=2*4.02

a=8.04

Bernardo Raditya
Sep 3, 2013
  • S = 1/4 mile = 1609/4 meters = 402.5 meters
  • S = V o 2 Vo^{2} × t \times t + 1/2 a t 2 t^{2} since the Vo = 0, so
  • S = 0 + 1/2 a 1 0 2 10^{2}
  • 402.5 = 50 × a 50 \times a
  • a = 402.5/50
  • a = 8.045

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