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January 28, 2015

January 28, 2015

Posted by **RJ** on Tuesday, May 26, 2009 at 9:36pm.

Find the speed of car 1 just before it collides with car 2.

Note: The correct answer does not depend on the variable: t

- Physics -
**TchrWill**, Friday, May 29, 2009 at 11:59amTwo stunt drivers drive directly toward each other. At time t=0 the two cars are a distance D apart, car 1 is at rest, and car 2 is moving to the left with speed Vo. Car 1 begins to move at t=0, speeding up with a constant acceleration Ax. Car 2 continues to move with a constant velocity.

Find the speed of car 1 just before it collides with car 2.

D = the distance between them at t = 0.

V2 = the constant velocity of car 2.

A = the constant acceleration of car 2.

x = the time of travel of car 2 to impact with catr 1.

t = the time of travel to impact.

1--t = x/V2 or x = tV2

2--D - x = At^2/2

3--D - x + x = D = At^2/2 + tV2

4--At^2/2 + tV2 - D = 0

5--At^2 + 2tV2 - 2D = 0

6--Using the quadratic equation,

---t = [sqrt(V2^2 + 2DA)- V2]/a

7--From Vf = Vo + At, the final velocity of car 1 at impact is

---Vf1 = sqrt(V2^2 + 2DA) - V2

Example:

D = 1000 miles

V2 = 100 miles/hr

A = 10 miles/hr^2

After a few guesses, x = 732 miles from which t = 7.32 hr, from which (D - x) = 268 miles which should equal AT^2/2 = 10(7.32)^2/2 = 268 miles and Vf = At = 73.2 mph.

Using Vf1 = sqrt(V2^2) + 2DA0) - V2,

Vf1 = sqrt((100^2) 2(1000)10 - 100 = 73.2mph.

Therefore, Vf1 = sqrt(V2^2 + 2DA) - V2

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