Inclined Plane Examples

Block on a Frictionless 30° Incline

A 10 kg block is placed on a smooth (frictionless) ramp inclined at 30∘30^\circ to the horizontal. Calculate the acceleration of the block down the ramp. (g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Block on a Frictionless 30° Incline Diagram

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Sliding Crate on a 25° Incline

A 5 kg wooden crate is on a 25∘25^\circ ramp. The coefficient of kinetic friction is μk=0.2\mu_k = 0.2. If it starts sliding from rest, what is its acceleration? (g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Sliding Crate on a 25° Incline Diagram

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Horizontal Push on a 40° Incline

A 20 kg block is on a 40∘40^\circ incline with μk=0.3\mu_k = 0.3. A person pushes it up the incline with a horizontal force P=300 NP = 300 \text{ N}. Find the block's acceleration up the ramp. (g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Horizontal Push on a 40° Incline Diagram

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Connected Objects (Tension & Pulleys)

Elevator Acceleration from Cable Tension

A 1000 kg elevator is being pulled upward by a cable. If the tension in the cable is 12,000 N, what is the upward acceleration of the elevator? (Assume g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Elevator Acceleration from Cable Tension Diagram

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Two Connected Blocks on a Frictionless Table

Block A (mA=4 kgm_A = 4 \text{ kg}) and Block B (mB=6 kgm_B = 6 \text{ kg}) are connected by a massless string on a frictionless horizontal table. A horizontal force F=30 NF = 30 \text{ N} pulls on Block B. Find the acceleration of the system and the tension in the connecting string.

Two Connected Blocks on a Frictionless Table Diagram

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Atwood Machine with Unequal Masses

An Atwood machine consists of two masses, m1=3 kgm_1 = 3 \text{ kg} and m2=5 kgm_2 = 5 \text{ kg}, connected by a massless string over a frictionless pulley. Find the acceleration of the masses and the tension in the string. (g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Atwood Machine with Unequal Masses Diagram

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Static vs. Kinetic Friction Examples

Horizontal Box with Kinetic Friction

A 50 kg box rests on a horizontal floor. A worker applies a horizontal pushing force of 200 N. The coefficient of kinetic friction between the box and the floor is μk=0.3\mu_k = 0.3. Determine the acceleration of the box. (g=9.8 m/s2g = 9.8 \text{ m/s}^2)

Horizontal Box with Kinetic Friction Diagram

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Static-Friction Motion Check

A 40 kg crate sits on a floor. The coefficient of static friction is μs=0.6\mu_s = 0.6 and kinetic friction is μk=0.4\mu_k = 0.4. A person pushes with 200 N200 \text{ N} of horizontal force. Does the crate move? If not, what is the force of static friction?

Static-Friction Motion Check Diagram

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Lawnmower Pushed Downward at 30°

A 25 kg lawnmower is pushed with a force of 150 N150 \text{ N} directed at a downward angle of 30∘30^\circ relative to the horizontal. If μk=0.2\mu_k = 0.2, what is its acceleration?

Lawnmower Pushed Downward at 30° Diagram

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Key Takeaways
  • When analyzing inclined planes, tilt your coordinate axes to align with the ramp to simplify calculations.
  • For connected objects (pulleys), the tension is uniform throughout an ideal massless string, and the magnitudes of acceleration are the same.
  • Static friction is an inequality (fs≤μsNf_s \le \mu_s N); it only provides enough force to prevent slipping. Kinetic friction is a constant value (fk=μkNf_k = \mu_k N).