Question

A particle is projected vertically upward with initial velocity of 20 metre per second find the time when it crosses 15 metre high mark

Answer 1

Answer:

given: u = 20 m/sec, s = 15 m, g = -10 m/sec

to find t

Explanation:

formula used : s = ut + 1/2at²

=> 15 = 20×t + 1/2×(-10)×t²

=> 15 = 20t - 5t²

=> 5t² - 20t + 15 = 0

=> t² - 4t + 3 = 0

=> t² - 3t - t + 3 = 0

=> t(t - 3) - 1(t - 3) = 0

=> (t - 1)(t - 3) = 0

=> t - 1 = 0 => t = 1 sec

=> t - 3 = 0 => t = 3 sec

Answer 2

Answer:

A particle is projected vertically upward with initial velocity of 20 metre per second find the time when it crosses 15 metre high mark in

t = 1 and 3 sec.