Forces and Newton’s Laws: Question 1

Worked solution

Step 1: Combine the forces along the same line

Both forces act on the skater along the same straight line but in opposite directions: $65\text{ N}$ forward (from the push) and $65\text{ N}$ backward (from air resistance). Forces acting in opposite directions along the same line are combined by subtraction:

$\text{Resultant force} = 65\text{ N} - 65\text{ N} = 0\text{ N}$

Step 2: Apply Newton’s first law

Newton’s first law tells us that an object continues at rest, or continues moving in a straight line at a constant speed, unless it is acted on by a resultant (unbalanced) force. Here, the two forces are equal and opposite, so the resultant force is zero.

Step 3: Decide what happens to the skater’s velocity

The skater was already moving at a constant velocity before this instant. Since the resultant force acting on her is zero, nothing changes: she simply continues moving at exactly the same constant velocity. She does not speed up, slow down, or stop.

Why the other options are wrong

Final answers

• Resultant force $=$ $0\text{ N}$
• The skater continues at her same constant velocity, option B