The cart is moving down the incline with a velocity v0 = 20 m/s at t = 0, at which time...

The cart is moving down the incline with a velocity v₀ = 20 m/s at t = 0, at which time the force P begins to act as shown. After 5 seconds the force continues at the 50-N level. Determine the velocity of the cart at time t = 8 s and calculate the time t at which the cart velocity is zero.