Practice question
Question
A ball is thrown upwards at 30m/s from a 40m tower. What is the time taken to reach a point 10m above the ground? (Take g\=10m/s2)
Explanation
Displacement y=−30m, −30=30t−5t2⇒5t2−30t−30=0⇒t2−6t−6=0. As per NCERT Chapter 3, equations v=u+at, s=ut+½at², v²=u²+2as describe uniformly accelerated motion. Applying correct signs and units gives 6.87 s as the result, so option A is correct.