If a projectile is fired straight up at a speed of 10 m/s,neglecting air resistance,the total time to return to its starting position is
A)1 s.
B)2 s.
C)10 s.
D)20 s.
E)not enough information

Question

Quizplus · Accepted Answer

The time it takes for a projectile to return to its starting position is equal to twice the time it takes to reach its maximum height. The maximum height reached by the projectile can be found using the formula 
h = (v^2)/2g, where v is the initial velocity and g is the acceleration due to gravity. 
Plugging in the given values, we get 
h = (10^2)/2(9.8) = 5.1 m 
The time it takes to reach this height can be found using the formula 
t = v/g 
Plugging in the given values, we get 
t = 10/9.8 = 1.02 s 
Therefore, the total time to return to the starting position is 2t = 2(1.02) = 2.04 s, which can be rounded to 2 s. So, the best choice is B.

If a Projectile Is Fired Straight Up at a Speed