📚 Learning Guide
Classical Mechanics Principles
hard

A 5 kg block is sliding on a horizontal surface with a coefficient of kinetic friction of 0.3. If the block is pushed with a force of 20 N to the right, what is the final velocity of the block after 2 seconds, assuming it starts from rest? Consider both Newton's Laws and the conservation of momentum in your calculations.

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Choose the Best Answer

A

5 m/s

B

5 m/s

C

0 m/s

D

0 m/s

Understanding the Answer

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Answer

The block’s weight is 5 kg, so the normal force is 5 kg × 9. 8 m/s² ≈ 49 N, making the kinetic friction force μₖN = 0. 3 × 49 ≈ 14. 7 N. The applied push is 20 N, so the net horizontal force is 20 N – 14.

Detailed Explanation

The applied force is only slightly larger than the frictional force, giving a small positive net force. Other options are incorrect because This answer assumes the block moves fast enough to reach 5 m/s, ignoring the friction that slows it; Like option A, it treats the applied force as if friction did not matter.

Key Concepts

Newton's Laws of Motion
Conservation of Momentum
Friction
Topic

Classical Mechanics Principles

Difficulty

hard level question

Cognitive Level

understand

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