A bullet shot straight up returns to its starting point in 10 s.What is the initial speed of the bullet,assuming no air?
A)9.8 m/s
B)25 m/s
C)49 m/s
D)98 m/s

Question

Quizplus · Accepted Answer

When a bullet is shot straight up, it will experience a constant downward acceleration due to gravity. The time taken for it to return back to the starting point is equal to the time taken for it to reach its maximum height and then fall back down. Therefore, the total time of flight is 10 s, which means it took 5 s to reach the maximum height.

Using the kinematic equation, 
Δy = v0t + (1/2)at²

where Δy is the displacement (which is zero as the bullet returns to its initial point), v0 is the initial velocity that we need to find, t is the time of flight (5 s to reach maximum height), and a is the acceleration due to gravity (-9.8 m/s²),

0 = v0(5) + (1/2)(-9.8)(5)²
v0 = 49 m/s

Hence, the initial speed of the bullet is 49 m/s. Therefore, the correct answer is choice C.

A Bullet Shot Straight Up Returns to Its Starting Point