A student investigates how the horizontal pulling force required to keep a wooden…
PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion
Problem
A student investigates how the horizontal pulling force required to keep a wooden block moving at constant speed depends on the block’s mass. The student records the following measurements:
• Trial 1: mass of block and added weights = 0.50 kg; steady pulling force = 0.70 N
• Trial 2: mass of block and added weights = 0.75 kg; steady pulling force = 1.05 N
• Trial 3: mass of block and added weights = 1.00 kg; steady pulling force = 1.40 N
Assume the tabletop is level and air resistance is negligible.
(a) Explain how the data support the claim that the magnitude of the kinetic-friction force is proportional to the magnitude of the normal force.
(b) Describe a method—based solely on these three measurements—for obtaining a numerical value for the coefficient of kinetic friction between the wood and the tabletop. Include a clear statement of any quantity you would calculate and how you would use the calculated value.
(c) Using principles of microscopic contact, explain why changing the surface area of the bottom of the wooden block (for example, by turning it on its side) would not be expected to change the coefficient obtained in part (b).