Final answer:
When an object is dropped, it undergoes free fall and is only influenced by gravity. Using the acceleration due to gravity, we can calculate the velocity of the object when it strikes the ground at the end of 3.9 seconds, which is approximately -38.22 m/s downward.
Step-by-step explanation:
When an object is dropped, it undergoes free fall, which means it is only influenced by gravity and not air resistance. The acceleration due to gravity on Earth is approximately 9.8 m/s². Using this acceleration, we can calculate the object's velocity when it strikes the ground at the end of 3.9 seconds.
Using the equation v = u + at, where v is the final velocity, u is the initial velocity (which is 0 in this case since the object is dropped), a is the acceleration due to gravity (-9.8 m/s² in the downward direction), and t is the time, we can substitute the given values and solve for v. In this case, t = 3.9 s:
v = 0 + (-9.8 m/s²) * 3.9 s = -38.22 m/s
Since the velocity magnitude is positive and the object was dropped from a high-rise dormitory, the velocity will be negative. Therefore, the object will be traveling at a speed of approximately 38.22 m/s downward when it strikes the ground.