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DESPRATE for help on PHYSICS, HELP ME?

this is one of many sample problems i have for homework and i dont understand them at all, can someone tell me how to do it so i can atleast try the rest? We have a test on this friday and i would like to know what im doing. thankss

  1. A speeder driving down the road at a constant 20 m/s, passes a patrolman parked roadside. The patrolman waits 3 secs, then pursues the speeder accelerating at a constant 4.0m/s(squared).

a. How long does it take for the patrolman to catch the speeder?

b. How far has he traveled before doing so?

Answers (2)

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speeder is initially 3 sec ahead - at 20 m/s this is a distance = (3)(20) = 60 m

in order to gain 60 m on the constant velocity speeder, the patrolman in the

SAME time = t must travel:

60 + 20t = 1/2at² {where a = 4.0}

60 + 20t = (0.5)(4.0)t²

0 = 2.0t² - 20t - 60

solve for positive root of t:

t = 12.4 s ANS

substitute t into either (60 + 20t) or (1/2at²) to find ans for b.