Question

*A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches 30° the box starts to slip and slides 4.0 m down the plank in 4.0 s. The coefficients of static and kinetic friction between the box and the plank will be, respectively:*

1️⃣ 0.6 and 0.5
2️⃣ 0.5 and 0.6
3️⃣ 0.4 and 0.3
4️⃣ 0.6 and 0.6​

Answer 1

• coefficient of statistic friction is = tan(30)

= 0.577 ~ 0.6

• and since coefficient os Kinetic friction will be less than static friction checking the options,

correct answer is option A) 0.6 and 0.5