Newton's Second Law Physics Example 4

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Example 4

medium
A 1500 kg1500 \text{ kg} truck accelerates at 1.2 m/s21.2 \text{ m/s}^2 while resistive forces total 300 N300 \text{ N} opposite the motion. What forward force must the engine provide?

Solution

  1. 1
    First find the required net force: Fnet=ma=1500×1.2=1800 NF_{\text{net}} = ma = 1500 \times 1.2 = 1800 \text{ N}
  2. 2
    The engine must overcome the 300 N300 \text{ N} resistive force and still leave 1800 N1800 \text{ N} net forward.
  3. 3
    So the engine force is Fengine=1800+300=2100 NF_{\text{engine}} = 1800 + 300 = 2100 \text{ N}

Answer

Fengine=2100 NF_{\text{engine}} = 2100 \text{ N}
Newton's second law applies to the net force, not just the applied force. When resistance is present, the engine must supply extra force beyond mama.

About Newton's Second Law

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, with the acceleration pointing.

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More Newton's Second Law Examples

Example 1 easy

A [formula] cart is pushed with a net force of [formula]. What is the acceleration of the cart?

Example 2 medium

A [formula] car accelerates from rest to [formula] in [formula]. What net force is required?

Example 3 hard

A [formula] block on a frictionless surface is pulled by a [formula] force at an angle of [formula]

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