The force required to start an object sliding across a uniform horizontal surface is larger than the force required to keep the object sliding at a constant velocity once it starts.
The magnitudes of the required forces are different in these situations because the force of kinetic friction is less than the force of static friction. <em>(d)</em>
I believe the answer is purple
Explanation:
At the top of the the ball's trajectory, there is only the horizontal component of the initial velocity, which is 
so the kinetic energy of the ball at this point is
![\;\;\;\;\;= \frac{1}{2}(0.15\:\text{kg})[(40\:\text{m/s})\cos30]^2](https://tex.z-dn.net/?f=%5C%3B%5C%3B%5C%3B%5C%3B%5C%3B%3D%20%5Cfrac%7B1%7D%7B2%7D%280.15%5C%3A%5Ctext%7Bkg%7D%29%5B%2840%5C%3A%5Ctext%7Bm%2Fs%7D%29%5Ccos30%5D%5E2)
