1. You are arguing over a cell phone while trailing an unmarked police car by 31
ID: 1661113 • Letter: 1
Question
1. You are arguing over a cell phone while trailing an unmarked police car by 31 m. Both your car and the police car are traveling at 100 km/h. Your argument diverts your attention from the police car for 2.0 s (long enough for you to look at the phone and yell, "I won't do that!"). At the beginning of that 2.0 s, the police officer begins emergency braking at 5 m/s2.
(a) What is the separation between the two cars when your attention finally returns? (Hint: This problem might be a bit easier to solve using the idea of relative velocity.)
_____ m
(b) Suppose it takes you another 0.4 s to realize your danger and begin braking. If you too brake at 5 m/s2, what is your speed when you hit the police car?
______ km/h
(c) How much time passes between your initial braking and the collision?
_______s
(d) How much distance do you cover during this time (i.e., while braking)?
_____m
2. You are to drive to an interview in another town, at a distance of 340 km on an expressway. The interview is at 11:15 A.M. You plan to drive at around 100 km/h, so you leave at 8:00 A.M. to allow some extra time. You drive at that speed for the first 100 km, but then construction work forces you to slow to 45 km/h for 40 km. What would be the least speed needed for the rest of the trip to arrive in time for the interview?
______km/h
y Noles ou are arguing over a cell phone while trailing an unmarked police car by 31 m. Both your car at!"L At the beginning of that 2.0 S, the police officer begins mergency braking at 5 mis- (a what is the ssdretion between the two cd's when our attention finally returns? Hint: This p'ublem r'«qh1 be d bit ees, tu sulve us nu the dea ur relative vedut (Hint: This problem migh yu to brake at 5 mys2, wha is your speed when you hit the police car? (b) Suppose it tekes you enother 0.4 s to realize your danger and begin braking 96.4008kh (CHow much time passas between yur iniial braking and the collision? (d) How much distance do you cover during this tima . wle braking)? Submit Anawer s. -1 points y Noles speed for You are to drive to an inter erin another town, at a distance o 340 km on an expressway he interview is at 11:15 A You plan to drive at a ound 100 m h so construction work forces you to slow to1m h for 40 km, what would be the least speed needed for the rest ofthe trip to arrive in time for the interven? ou eave at 8:00 A. to a o some extra tme. You drive at that he first 100 km, but then kcmy/hExplanation / Answer
2.
Total time = 11:15 AM - 8:00 AM = 3 hr 15 min
time needed at speed of 100 km/hr
t1 = 100/100 = 1 hr
time needed at speed of 45 km/hr
t2 = 40/45 = 0.89 hr
Time remaining = 3.25 hr - 1 hr - 0.89 hr = 1.36 hr
distnace remaining = 340 - 100 - 40 = 200 km
So speed for this distance should be
V = 200/1.36 = 147.05 km/hr
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