Summary
Highlights
The video introduces a problem: calculate the resultant force on a car of mass 2,000 kg that slows from 20 m/s to 5 m/s in 15 seconds.
The first method uses the rate of change of momentum (Force = ΔP/Δt). The change in momentum (ΔP) is calculated as M × ΔV (mass multiplied by change in velocity). The final velocity is 5 m/s, the initial velocity is 20 m/s, and the mass is 2,000 kg. This results in a change in momentum of -30,000 kg m/s.
The change in time (Δt) is 15 seconds. Dividing the change in momentum (-30,000 kg m/s) by the change in time (15 seconds) yields a resultant force of -2,000 Newtons. The negative sign indicates the force acts in the opposite direction to the car's motion.
The alternative method uses Newton's Second Law (F=ma). First, acceleration (a) is calculated as (v-u)/t, which is (5 m/s - 20 m/s) / 15 seconds, resulting in -1 m/s². With the mass still being 2,000 kg, applying F=ma gives a force of 2,000 kg × -1 m/s² = -2,000 Newtons.
Both methods provide the same correct answer, confirming that either approach is valid for solving this type of problem.