Friction (static and kinetic) Knowledge-Based Practice

Questions

1. 1.

   A 3 kg block resting on a rough horizontal table is connected by a light string passing over a frictionless pulley to a hanging 1 kg block. If the coefficient of kinetic friction between the 3 kg block and the table is 0.20, what is the magnitude of the acceleration of the system once released? (Take $g = 10\text{ m/s}^2$.)

   • A) $2.5\text{ m/s}^2$
   • B) $2.0\text{ m/s}^2$
   • C) $1.0\text{ m/s}^2$
   • D) $0.5\text{ m/s}^2$
2. 2.

   A 10 kg box is pushed across a level floor by an applied force of 50 N directed at an angle of 37° below the horizontal. If the coefficient of kinetic friction between the box and the floor is 0.20, what is the magnitude of the kinetic friction force acting on the box? (Take $g = 10\text{ m/s}^2$, $\sin 37^\circ = 0.60$, and $\cos 37^\circ = 0.80$.)

   • A) 14 N
   • B) 20 N
   • C) 26 N
   • D) 28 N
3. 3.

   A crate rests on the flat horizontal bed of a truck that is accelerating along a level road. If the coefficient of static friction between the crate and the bed is 0.40 and the coefficient of kinetic friction is 0.25, what is the maximum acceleration the truck can have without the crate slipping? (Take $g = 10\text{ m/s}^2$.)

   • A) $4.0\text{ m/s}^2$
   • B) $2.5\text{ m/s}^2$
   • C) $1.5\text{ m/s}^2$
   • D) $6.5\text{ m/s}^2$
4. 4.

   A 10 kg block rests on a level horizontal floor where the coefficient of static friction is 0.75. What minimum tension applied at an angle of 37° above the horizontal is required to begin moving the block? (Take $g = 10\text{ m/s}^2$, $\sin 37^\circ = 0.60$, and $\cos 37^\circ = 0.80$.)

   • A) 60 N
   • B) 75 N
   • C) 48 N
   • D) 80 N
5. 5.

   A sled traveling horizontally at an initial speed of 12 m/s slides across a level patch of rough ice and comes to rest due to friction. If the coefficient of kinetic friction between the sled and the ice is 0.24, what distance does the sled slide before stopping? (Take $g = 10\text{ m/s}^2$.)

   • A) 30 m
   • B) 60 m
   • C) 50 m
   • D) 25 m
6. 6.

   A block slides down a rough inclined plane angled at 37° above the horizontal at a constant velocity. What is the coefficient of kinetic friction between the block and the incline? (Take $\sin 37^\circ = 0.60$ and $\cos 37^\circ = 0.80$.)

   • A) 0.45
   • B) 0.60
   • C) 0.75
   • D) 0.80
7. 7.

   A 6 kg box is pulled across a horizontal surface at a constant velocity by a horizontal force of 24 N. If an additional 2 kg mass is placed on top of the box, what horizontal force is required to maintain the same constant velocity across the surface? (Assume g = 10 m/s².)

   • A) 24 N
   • B) 28 N
   • C) 32 N
   • D) 40 N
8. 8.

   A 3 kg wooden block is held against a vertical wall by an applied horizontal force $F$. If the coefficient of static friction between the block and the wall is 0.25, what is the minimum magnitude of $F$ required to prevent the block from slipping downward? (Take $g = 10\text{ m/s}^2$.)

   • A) 120 N
   • B) 75 N
   • C) 30 N
   • D) 7.5 N
9. 9.

   A 2 kg crate rests on a horizontal floor where the coefficient of static friction is 0.60 and the coefficient of kinetic friction is 0.40. If a constant horizontal force of 18 N is applied to the crate, what is the magnitude of its acceleration? (Assume g = 10 m/s².)

   • A) 3 m/s²
   • B) 5 m/s²
   • C) 6 m/s²
   • D) 9 m/s²
10. 10.

    A 4 kg block rests on a horizontal floor with coefficients of static and kinetic friction of $\mu_s = 0.50$ and $\mu_k = 0.30$. If a horizontal pulling force of 15 N is applied to the block, what is the magnitude of the friction force acting on it? (Use $g = 10\text{ m/s}^2$.)

    • A) 12 N
    • B) 20 N
    • C) 15 N
    • D) 0 N

Answers and step-by-step solutions appear after you finish the test.