Answer:
4 s
Step-by-step explanation:
The following data were obtained from the question:
Initial velocity (u) = 19.4 m/s.
Acceleration due to gravity (g) = –9.81 m/s²
Total time (T) =.?
Next, we shall determine the time take by the rock to get to the maximum height. This can be obtained as follow:
NOTE: At maximum height, the final velocity is zero.
Initial velocity (u) = 19.4 m/s.
Acceleration due to gravity (g) = –9.81 m/s²
Final velocity (v) = 0 m/s
Time taken to reach the maximum height (t) =.?
v = u + gt
0 = 19.4 + (–9.81 × t)
0 = 19.4 – 9.81t
Collect like terms
0 – 19.4 = –9.81t
–19.4 = –9.81t
Divide both side by –9.81
t = –19.4 / –9.81
t ≈ 2 s
Thus, it took approximately 2 s for the rock to reach its maximum height.
Finally, we shall determine the total time spent by the rock in the air as follow:
Time taken to reach the maximum height (t) = 2 s
Total time spent in air (T) =?
The total time (T) spent by the rock in the air will be two times the time taken (t) to reach the maximum height i.e
T = 2t
t = 2 s
T = 2 × 2
T = 4 s
Therefore, the rock spent approximately 4 s in the air.