While the cart is moving along an aisle, it comes in contact with a smear of margarine that had recently been dropped on the floor. Suddenly the friction force is reduced from -40.0 newtons to -20.0 newtons. What is the net force on the cart if the “pushing force” remains at 40.0 newtons? Does the grocery cart move at constant velocity over the spilled margarine? Identify the normal force on the shopping cart after 75 newtons of groceries are added to the cart.

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction 

Answershe should not have multiplied the sulfur atoms by the subscript 4

2.77 x 10^-3 its for plato user 

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.