Theory question 108
DynamicsAn object is projected vertically upwards with a velocity of 80 ms−1. Find the;
(a) maximum height reached; (b) time taken to return to the point of projection. [Take g = 10 ms−2]
Show the model answer
Model answer
(a) At the top v = 0: 0 = 80² − 2(10)s, so s = 6400/20 = 320 m
(b) Time to the top: 0 = 80 − 10t, t = 8 s
Time to return = 2 × 8 = 16 s
Explanation
Use v² = u² − 2gs for the height and v = u − gt for the time up; the time down is the same.