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# Tag Archives: coefficient of kinetic friction

## A few numerical problems from laws of motion

- A worker pulls a 200. N packing crate with an applied force of 55.0 N. The crate accelerates at a rate of 0.250 m/s(squared). What is the coefficient of kinetic friction between the crate and the factory floor?
- A student pulls a 150. N sled up a 28 degree slope at a constant speed by applying a force of 100. N. Near the top of the hill he releases the sled. With what acceleration does the sled go down the hill?
- A 200. N crate rests on a ramp; the maximum angle just before it slips is 25 degrees with the horizontal. What is the coefficient of static friction between the crate and the surface of the ramp?
- A man pulls a sled with a weight of 200. N with a constant velocity across a horizontal snow surface. If a force of 80N is being applied to the sled rope at an angle of 53 degrees to the ground, what is the coefficient of friction between the sled and the ground?
- A jet plane is flying with a constant speed along a straight line at an angle of 30degree above the horizontal. The weight of plane is 86 500N. Its engine provides a forward thrust T of 103 000N. The lift of force L(directed perpendicular to the wings)and the force R of air resistance (directed opposite to the motion)act on the plane. Find L & R

## A numerical from Projectile motion, friction and more

**Hale asked:**

One side of the roof of a building slopes up at 33.5°. A roofer kicks a round, flat rock that has been thrown onto the roof by a neighborhood child. The rock slides straight up the incline with an initial speed of 15.0 m/s. The coefficient of kinetic friction between the rock and the roof is 0.430. The rock slides 10.0 m up the roof to its peak. It crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof, with negligible air resistance. Determine the maximum height the rock reaches above the point where it was kicked.

**(The question is left for visitors to answer.)**