Pulling force supplies energy for kinetic energy gain

Steps:

• Object accelerates right on horizontal ground, so net horizontal force acts right.
• Forces include pulling force right, frictional force left, weight down, contact (normal) force up.
• Displacement horizontal, so vertical forces (weight, contact) do zero work as perpendicular to motion.
• Net work equals change in kinetic energy; pulling force provides positive work F_p × d, overcoming friction to enable acceleration.

Why C is correct:

• By work-energy principle, work done by pulling force (F_p × d) inputs energy that increases kinetic energy after accounting for frictional losses.

Why the others are wrong:

• A: Contact force (normal) is perpendicular to displacement, so work is zero.
• B: Frictional force opposes motion, doing negative work that dissipates energy.
• D: Weight is perpendicular to horizontal displacement, so work is zero.

Final answer: C