Question

An object moves along a straight line so that at any time t , for 0≤t≤8 , its position is given by x(t)=5+4t−t2 . For what value of t is the object at rest?
A. t = 2
B. t = 4
C. t = 9/2
D. t = 5

Answer 1

It’s ccccccccccccccccccccccc

Answer 2

Answer:

D. t = 5

when the object is at rest => x(t) = 0

<=> -t^2 + 4t + 5 = 0

<=> t^2 - 4t - 5 = 0

<=> (t - 5)(t + 1) = 0

=> t = 5 or t = -1

but t》0

=> t = 5