A point starts with the velocity 10 cm/sec and moves along a straight line with uniform acceleration 5cm/sec2. How much time it takes to describe 80 cm?

A point starts with the velocity 10 cm/sec and moves along a straight line with uniform acceleration 5cm/sec2. How much time it takes to describe 80 cm? Correct Answer 4 seconds

Let us assume that the point takes t seconds to describe a distance 80 cm. Then using the formula s = ut +1/2(ft2) we get, 80 = 10*t + 1/2(5)(t2) Or 5t2 + 20t – 160 = 0 Or t2 + 4t – 32 = 0 Or (t – 4)(t + 8) = 0 Or t = 4 Or -8 Clearly, t = -8 is inadmissible. Therefore, the required time = 4 seconds.
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