Question

An object A moving horizontally with kinetic energy of 800 J experiences a constant opposing force of 100 N, while moving from a place x to a place y, where xy is 2 m. What is the energy of A at y?

• A. 700 J
• B. 400 J
• C. 600 J
• D. 300 J

Hint:

Opposing forces reduce kinetic energy. Always use negative work for resistive forces.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
According to the Work-Energy Theorem, the work done by all forces on an object is equal to the change in its kinetic energy.
An opposing force does negative work, which reduces the total energy of the object.
: Key Formula or Approach:
1. Work done by opposing force \( W = -F \times d \).
2. Final Energy \( E_y = E_x + W \).
Step 2: Detailed Explanation:
Initial kinetic energy at x, \( E_x = 800 \text{ J} \).
Opposing force \( F = 100 \text{ N} \).
Distance between x and y, \( d = 2 \text{ m} \).
The work done by the opposing force is:
\[ W = -F \times d \]
\[ W = -(100 \text{ N}) \times (2 \text{ m}) = -200 \text{ J} \]
The energy at place y is calculated by adding the work done to the initial energy:
\[ E_y = 800 \text{ J} + (-200 \text{ J}) \]
\[ E_y = 600 \text{ J} \]
Step 3: Final Answer:
The energy of object A at place y is 600 J.