The coefficient of static friction between a 40kg crate and a concrete surface is 0.25. Find the magnitude of the minimum force needed to keep the crate stationary on the concrete base inclined at 45° to the horizontal

John Perolski
September 03, 2023

 Physics Jamb, Waec, Neco Past Questions & Answers on FRICTIONAL FORCE


QUESTIONS 9: The coefficient of static friction between a 40kg crate and a concrete surface is 0.25. Find the magnitude of the minimum force needed to keep the crate stationary on the concrete base inclined at 45° to the horizontal. 

A. 400N 

B. 300N 

C. 283N 

D. 212N (g = 10m/s) 

Ans :212 N JAMB 1987 

SOLUTIONS 

μ = 0.25

m = 40kg

θ = 45°

Minimum force = ?

Minimum force = R - P

Vertical components = Rsinθ

Horizontal components = Fcosθ = μRcosθ

but R = W = mg

Minimum force = Rsinθ - μRcosθ

Fm = (40 x 10 x sin 45) - (40 x 10 x 0.25 x cos 45)

FM = 212N