A 65.0-kg crate is sitting on the ground when an external force is applied. The

Question

A 65.0-kg crate is sitting on the ground when an external force is applied. The coefficient of kinetic friction for these surface is 0.12, and the coefficient of static friction for these surfaces is 0.20. For each scenario described below, determine if the friction on the crate will be static or kinetic and calculate the magnitude of the friction.

a) A 1.0 × 102-N force is applied to the stationary crate for 10 seconds. After 5 seconds,

b) A 150-N force is applied to the stationary crate for 10 seconds. After 5 seconds,

c) A 150-N force is applied to the moving crate for 10 seconds. After 5 seconds,

Explanation / Answer

A) maximum static friction = us mg = 0.20*65*9.8 =127.4

Since applied force is less than this, Friction is static.

Friction = 100 N

B) Ii is more than maximum static friction, so friction will be kinetic.

Friction = uk mg = 0.12*65*9.8 = 76.44 N

C) since it is moving, Friction is kinetic

Friction = uk mg = 76.44 N

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