LON-CAPA Stopping a Car Consider a bead starting at rex Consider A Bead Starting
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LON-CAPA Stopping a Car Consider a bead starting at rex Consider A Bead Starting At i × v N how to screen sht on mac c secure https: capa8.phy ohio ed es/fsu openstax-CollegePhysics 07 wor EnergyPower12 Work EnergyTheorem problem?symb-uploaded%2fohou%2f91391 8041 50295a490 Megan Michalak(Student- section: 101) Physics 2001/Spring 2018 l Messages Courses Help Logout Main Menu Contents Grades Course Contents» * Assignment 7 Stopping a Car O Timer Notes Evaluate EeFeedback-Print Info Stopping a Car Due in 3 hours, 39 minut Calculate the force needed to bring a 820-kg car to rest from a speed of 73.0 km/h in a distance of 137 m (a fairly typical distance for a non-panic stop). -1.52N SubmAnewer Incorrect. Tries 1/10 Previous Tries Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 1.78 m. Calculate the force exerted on the car and compare it with the force found in part (a). Force = Ratio = Submit Answer Tries 0/10 is discussion is closed 4. Send FeedbackExplanation / Answer
a)
vi = 0
vf = 73 km/h
= 73*5/18 m/s
= 20.28 m/s
d = 137 m
acceleration of the car, a = (vf^2 -vi^2)/(2*d)
= (20.28^2 - 0^2)/(2*137)
= 1.501 m/s^2
Forc needed, F = m*a
= 820*1.501
= 1231 N
b)
acceleration of the car when it stops with in 1.78 m, a = (vf^2 - vi^2)/(2*d)
= (0^2 - 20.28^2)/(2*1.78)
= -155.5 m/s^2
Force exerted by the concrete wall, F' = m*|a|
= 820*155.5
= 127510 N
c) ratio, F'/F = 127510/1231
= 103
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