A simple Physics question?

Question

A car traveling at 18.0 m/s comes to a stop in 5.0 seconds. How far did it travel?

Answer 1

Assuming uniform decceleration

easier to work it backwards, how far does it travel accelerating to 18 m/s in 5 sec

d = ½at²  = ½18(5)² = 225 meters

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Answer 2

If he likes stopping by hitting brick walls then he travels

18 (m/s)*5(s) = 90 m

If he likes stopping by uniformly decelerating then we first need to find the acceleration that will bring his velocity to zero in 5 (s).

a = -18/5 (m/s^2)

In that case the total distance traveled is

d = v*t + 1/2 a t^2

d = 18*5 - 1/2* 18/5 *5^2

d = 18*5 - 1/2 18*5 = 9*5 = 45 m

Answer 3

There is an easy way to solve this, but, as usual, it takes some explaining:

For constant deceleration, let:

v = final velocity

u = initial velocity

t = time

a = acceleration

Use the basic formulas:

a = (v - u)/t

v² = u² + 2ax

Solve for x:

x = (v² - u²) / (2(v - u)/t)

x = t (v² - u²) / 2(v - u)

Since v = 0, this simplifies to:

x = t (- u²) / -2u

x = ut/2

x = 18 * 5 /2

x = 45 m

I liked what halfeatenpizza wrote about hitting brick walls. ROFL. Thumbs up.

Answer 4

S=vt     Distance=velocity*time    S=18*5 =90metres