Answer:
-7.14
Explanation:
According to equation of motion
v = u + at
where
v is the final velocity at any time t
u is the initial velocity
a is the acceleration
and t is the time
___________________________________________
Given
An object is thrown upward it means
its initial velocity is in upward direction
but acceleration due to gravity is in downward direction which will cause to decrease the velocity of object.
Intial velocity u = 31.1 m/s
final velocity v at 4 second we have to find.
t = 4 second
a = g = 9.81 m/s2 (it is acting in opposite direction of motion hence its sign will be negative ).
Thus
a = - 9.81 m/s2
using the above values in v = u + at
v = 32.1 - 9.81*4
v = 32.1 - 39.24
v = -7.14
Thus, correct option is -7.14.
