Your car has stalled and you need to push it. you notice as the car gets going that you need less and less force to keep it going. suppose that for the first 15 m your force decreased at a constant rate from 210 n to 45 n. how much work did you do on the car?

675 Joules

Explanation:

Considering that work can be calculated with the following formula:

W = Fx D

Where:

W = work

F = force

D = distance

We can directly use this formula in case the applied force remains constant

In case the force does not remain constant, we can calculate the work as a change, this is :

ΔW = ΔFxΔD

For this scenario, we have:

W₁ = F₁xD₁

F₁ = 210 N, D = 0 m

W₁ = 210Nx0m = 0 Joules

W₂ = F₂xD₂

F₂ = 45 N , D₂ = 15 m

W₂ = 45Nx15m = 675 Joules

Finally: ΔW = Total work performed when moving the car 15 m

ΔW = W₂ - W₁ = 675 Joules - 0 Joules = 675 Joules

need to see circuit to get time constant