A small cart of mass m is pushed to the right across a horizontal track by a constant force Fp applied by a rod connected to a motor. Simultaneously, a string pulls on the cart with a force T that is directed upward and to the left, making an angle ϕ above the horizontal. The coefficient of kinetic friction between the cart and the track is μk. Which of the following descriptions best represents a correct free-body diagram for the cart?
a) Rightward push Fp; vertical upward tension T; weight downward; normal force upward; kinetic friction leftward
b) Rightward push Fp; upward-left tension T at angle ϕ; weight downward; normal force upward; kinetic friction leftward
c) Rightward push Fp; upward-left tension T at angle ϕ; weight downward; normal force upward; kinetic friction rightward
d) Rightward push Fp; upward-left tension T at angle ϕ; weight downward; kinetic friction leftward