Question

on his way to class, a student on a skateboard is accelerating on a downhill stretch. which of the following statements is true? (select all that apply.)
the skateboarder is moving in the direction of the net force.
the skateboarders acceleration is perpendicular to the net force.
the skateboarders acceleration is in the direction of the net force.
the skateboarder is subjected to a net external force in the direction of motion.

Explanation:

According to Newton's second law \(F = ma\), the direction of acceleration \(a\) is the same as the direction of the net force \(F\). Since the skateboarder is accelerating, there must be a net external force. If the skateboarder is accelerating downhill, the net force is in the direction of motion (downhill).

1. For the first option:

• If there is a net force, and the skateboarder is accelerating (changing velocity), the general motion (when starting from rest or having an initial velocity in the same - direction as the net force) will be in the direction of the net force.

1. For the second option:

• From \(F = ma\), \(a=\frac{F}{m}\) (where \(m\) is the mass of the skate - boarder). The direction of \(a\) is the same as the direction of \(F\), not perpendicular.

1. For the third option:

• By Newton's second law \(F = ma\), the acceleration \(a\) and the net force \(F\) have the same direction.

1. For the fourth option:

• Since the skateboarder is accelerating (\(a

eq0\)), from \(F = ma\) (\(m>0\)), \(F
eq0\). And because the acceleration is in the direction of motion (downhill stretch), the net external force is in the direction of motion.

Answer:

• The skateboarder is moving in the direction of the net force.
• The skateboarder's acceleration is in the direction of the net force.
• The skateboarder is subjected to a net external force in the direction of motion.