Question

an object thrown vertically upwards reaches a height of 500 m. what was its initial velocity? how long will the object take to come back to the earth? assume g = 10 M per second square

Answer 1

Using Newton's law of motion,
$v^{2} - u^{2} =2as$

where v is the final velocity ( equal to zero ), u is the initial velocity a is the acceleration and s is the distance traveled.

0 - u*u = -2 * 10 * 500
u = 100 m/s

Using Newton's law of motion,
 v = u + at

 (Where v is the final velocity, u is the initial velocity, a is the acceleration and t is the time taken)


Putting in values (Final velocity is taken to be 0, and a = 10m/s (gravity) with upwards direction to be positive),
we get

0 = 100 - 10 * t 
t = 10 seconds

This is the upward travel time of the ball. Downwards travel time is equal to this. So the ball will come back to earth in a total of 20 seconds.