A person riding in the back of a pickup truck traveling at 60km/h on a straight, level road throws a ball with a speed of 10km/h relative to the truck in the direction of the truck's motion.

To determine the overall velocity of the ball, we need to consider the velocities of the ball relative to both the truck and the ground.

Let's analyze the scenario step by step:

1. The pickup truck is traveling at 60 km/h.
2. The person inside the truck throws the ball with a speed of 10 km/h relative to the truck.

To find the velocity of the ball relative to the ground, we can add the velocities of the ball and the truck. Since the ball is thrown in the same direction as the truck's motion, we can add the velocities directly:

Ball's velocity relative to the ground = Truck's velocity + Ball's velocity relative to the truck

Given:
Truck's velocity = 60 km/h
Ball's velocity relative to the truck = 10 km/h

Adding the velocities:
Ball's velocity relative to the ground = 60 km/h + 10 km/h

Therefore, the ball's velocity relative to the ground is 70 km/h.

Explanation on how to calculate the overall velocity of an object involves adding the velocities of the object and its reference point. In this case, we added the velocity of the ball relative to the truck and the velocity of the truck itself to find the overall velocity of the ball relative to the ground.