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
The value of t if the object at rest is 2 secs: Option A is correct
Given the position of the object moving in a straight line expressed as:
x(t)=5+4t−t²
The velocity of the body at rest is zero
Get the velocity fucntion.
v(t) = d(x(t))/dt = 4 - 2t
Since v(t) = 0
0 = 4 - 2t
-4 = -2t
t = 2
Hence the value of t if the object at rest is 2 secs
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