the terminal velocity of a tennis ball is about 21 m/s. a tennis ball is dropped from a hot air balloon. how fast will it be moving after falling for 10 s? 21m/s, 77m/s, 9.8m/s, or 98m/s.

v = g t = 9.81 * 10 = 98.1 if no air drag

but with friction terminal speed is 21
so
21 m/s

To determine the speed of the tennis ball after falling for 10 seconds, we need to consider its acceleration due to gravity. At the beginning, the ball will experience a constant downward acceleration of approximately 9.8 m/s² until it reaches its terminal velocity.

Since the tennis ball has already reached its terminal velocity of 21 m/s, it will not accelerate further. Therefore, if the ball has fallen for 10 seconds, it will still be moving at a speed of 21 m/s because it has already reached its maximum velocity.

So, the correct answer is 21 m/s.

To find how fast the tennis ball will be moving after falling for 10 seconds, we can use the concept of terminal velocity.

Terminal velocity is the maximum velocity that an object can achieve while falling through a fluid (in this case, air) due to the balance of two forces: gravity pulling the object downward and air resistance pushing against it.

The question states that the terminal velocity of a tennis ball is about 21 m/s. This means that after reaching this speed, the air resistance pushing upward will be equal to the force of gravity pulling downward, resulting in a constant velocity.

Since the tennis ball is only falling for 10 seconds, it has not had enough time to reach its terminal velocity. Therefore, the speed of the tennis ball after falling for 10 seconds will not be equal to its terminal velocity of 21 m/s.

Instead, the speed of the tennis ball after falling for 10 seconds will be dependent on the acceleration due to gravity, which is approximately 9.8 m/s^2. In the absence of significant air resistance, an object in free fall will continue to accelerate at this rate.

Using the equation for uniformly accelerated motion, we can calculate the speed of the tennis ball after falling for 10 seconds:

v = u + at

Where:
v = final velocity
u = initial velocity (which is 0 since the ball was dropped)
a = acceleration due to gravity (which is 9.8 m/s^2)
t = time (which is 10 seconds)

Plugging in the values:

v = 0 + (9.8 m/s^2) * (10 s)
v = 0 + 98 m/s

Therefore, the tennis ball will be moving at a speed of 98 m/s after falling for 10 seconds.

So the correct answer is 98 m/s.