A construction worker riding in the tray of a truck traveling at 10 m/s, sees one of his friends passing and decides to jump off the truck. The magnitude of his

initial speed of jumping is:
(a) zero
(b) Less than the truck's
(c) Equal to that of the truck
(d) Greater than that of the truck

a. Zero.

In order to determine the magnitude of the construction worker's initial speed of jumping, we need to consider the concept of relative velocities.

When the construction worker jumps off the truck, he will initially have the same velocity as the truck because he is still in the tray and moving with the truck. Therefore, his initial speed of jumping is equal to the truck's velocity, which is 10 m/s.

So, the correct answer is (c) Equal to that of the truck.