16. 0/1 points I Previous Answers SerPSE10 2.7.OP 017 My Notes Ask Your Teacher

Question

16. 0/1 points I Previous Answers SerPSE10 2.7.OP 017 My Notes Ask Your Teacher (a) The driver of a car slams on the brakes when he sees a tree blocking the road. The car slows uniformly with acceleration of -5.40 m/s2 for 4.15 s, making straight skid marks 63.4 m long, all the way to the tree. With what speed (in m/s) does the car then strike the tree? to calculate the initial velocity of the car first. What If? If the car has the same initial velocity, and if the driver slams on the brakes at the same distance from the tree, then what would the acceleration need to be (in m/s2) so that the car narrowly avoids a collision? (b) m/s2

Explanation / Answer

(a)

From the kinematic equation,

s = ut + (1/2)at2

63.4 = u*4.15 - (1/2)*5.4*(4.15)^2

u = 26.48 m/s

Speed when car strike the tree,

v = u + at

v = 26.48 - 5.4*4.15

v = 4.072 m/s

(b)

a = -5.4 m/s^2

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