Three weeks is how long a human can live without food
When you drop a ball, it is dropped DOWNWARDS so the number is represented by a negative number. If you toss the ball up it will be a positive number.
To answer your question:
When an object is dropped downwards there will be a negative number since the object is falling downwards.
Lymphoid organs in the immune system, includes the bone marrow
Velocity is a vector quantity which means it has both magnitude and direction means in order to calculate it another vector quantity is used which is displacement on the other hand speed is a scalar quantity.
