NCERT Solutions for Class 9 Science Chapter 11
Important NCERT Questions
Work and Energy
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-158
Questions No-4
Certain force acting on a 20 kg mass changes its velocity from 5 m s^–1 to 2 m s^–1. Calculate the work done by the force.
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Given:
– Mass (m) = 20 kg
– Initial velocity (v_initial) = 5 m/s
– Final velocity (v_final) = 2 m/s
1. Work-Energy Principle:
– The work done (W) on an object is equal to the change in its kinetic energy (Δ KE).
2. Change in Kinetic Energy:
– The change in kinetic energy (Δ KE) formula is:
Δ KE = 1/2 x m x ( v²_final – v²_initial)
3. Calculation:
– Substituting the given values into the formula:
Δ KE = 1/2 x 20 kg x (2 m/s)² – (5 m/s)²
Δ KE = -210J
4. Result and Interpretation:
– The change in kinetic energy is -210 J
– Since work done is equal to the change in kinetic energy, the work done by the force is also -210 J
– The negative sign indicates that the work done by the force results in a decrease in the object’s kinetic energy.
Understanding these steps illustrates how the work done by a force can be calculated using the change in kinetic energy, providing insight into the change in energy associated with the object’s changing velocities due to the force applied.