A rock is thrown horizontally off of a cliff with a velocity of 20 m/s. The rock lands 60 m from the base of the cliff. How long will the rock be in the air?

The time spent by the rock in air is 3 s.

Explanation:

Given;

initial  horizontal velocity of the rock, u = 20 m/s

horizontal distance traveled by rock, R = 60 m

The the range of the projectile is given by;

R = vt

where;

v is the initial  horizontal velocity of the rock

t is the time spent by the rock in air

t = R/v

t = 60 / 20

t = 3 s

Therefore, the time spent by the rock in air is 3 s.

the one with the highest speed

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.