A ball is dropped from a rooftop of a building and falls for two seconds. The acceleration of gravity is 9.8 m/s2. The ball is referred to at the two-second time.
-The velocity of the ball in m/s is
A)0.
B)4.9.
C)9.8.
D)19.6.
E)none of these.

Question

A ball is dropped from a rooftop of a building and falls for two seconds. The acceleration of gravity is 9.8 m/s2. The ball is referred to at the two-second time. 
-The velocity of the ball in m/s is
A)0.
B)4.9.
C)9.8.
D)19.6.
E)none of these.

Quizplus · Accepted Answer

The velocity of the ball can be calculated using the formula:
v = u + at 
where, 
u = initial velocity (0 m/s as the ball was dropped)
a = acceleration due to gravity = 9.8 m/s2 (negative as the acceleration is downwards)
t = time taken = 2 seconds

Therefore, 
v = 0 + (-9.8 x 2) 
v = -19.6 m/s

As velocity is a vector quantity, we take its magnitude, which is positive. 
So, the velocity of the ball after 2 seconds of falling is 19.6 m/s, in the downward direction. 
Therefore, the correct answer is D) 19.6.

A Ball Is Dropped from a Rooftop of a Building