A 300-kg crate is placed on an adjustable inclined plane. As one end of the incl

Question

A 300-kg crate is placed on an adjustable inclined plane. As one end of the incline is raised, the crate begins to move downward. If the crate slides down the plane with an acceleration of 0.70 m/s^2 when the incline angle is 25 degree, what is the coefficient of kinetic friction between ramp and crate? (g = 9.8 m/s^2) a. 0.47 b. 0.42 c. 0.39 d. 0.12 Doug hits a hockey puck, giving it an initial velocity of 6.0 m/s. If the coefficient of kinetic friction between ice and puck is 0.050, how far will the puck slide before stopping? a. 19 m b. 25 m c. 37 m d. 57 m A 9.0-kg hanging weight is connected by a string over a pulley to a 5.0-kg block sliding on a flat table. If the coefficient of sliding friction is 0.20, find the tension in the string. a. 19 N b. 24 N c. 32 N d. 38 N A rock is thrown straight up with an initial velocity of 15.0 m/s. Ignore energy lost to air friction. How high will the rock rise? a. 153 m b. 22.9 m c. 6.50 m d. 11.5 m

Explanation / Answer

From Newton's second law:

n = mgcos@

ma = mgsin@-fk

ma = mgsin@ - un

ma = mgsin@ - umgcos@

coefficient of kinetic friction:

  umgcos@ = mgsin@ - ma

u= [gsin@ - a]/gcos@

= [9.8*sin25o - 0.70] / 9.8*cos25o

= 0.3875

= 0.39

option c is correct.

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