Torque from forces on opposite sides of lid

Steps:

• Convert radius to meters: r = 4.0 cm = 0.04 m.
• Two equal forces F act tangentially on opposite sides, each at lever arm r.
• Total torque τ = 2 F r = 20 Nm.
• Solve for F: F = τ / (2 r) = 20 / (2 × 0.04) = 250 N.

Why C is correct:

• Torque formula for two diametrically opposite tangential forces gives τ = 2 F r, yielding F = 250 N.

Why the others are wrong:

• A: 5 N underestimates by factor of 50, likely from unit confusion or division error.
• B: 50 N results from using r = 4 cm without converting to meters.
• D: 500 N assumes single force, ignoring the two-side application (τ = F r).

Final answer: C