Calculate Magnitude of Impulse on 920-kg Car

[RevX]

Homework Statement

What is the magnitude of the Impulse exerted on a 920-kg car as it slows from 24.3 m/s to 12.9 m/s while traveling in a straight line?

The Attempt at a Solution

I was thinking 920(24.3 m/s) and 920(12.9 m/s) and subtract the two.

Not totally sure tho.

 

[Rawrr!]

The Impulse in classical mechanics can be understood as the average force multiplied by the time it is exerted.

J = F_average (t₂ - t₁ )

J = ∫ F dt , evaluated from t₁ to t₂

since F is related to the change in momentum with respect to time,

J = ∫ (dp/dt) dt , evaluated from t₁ to t₂

here, the dt's cancel, and you get,

J = ∫ dp , evaluated from P₁ to P₂

so, finally you get to J = p₂ - p₁ = ΔP

You suggested subtracting the two. Make sure to subtract them in the correct order to obtain the correct sign.