Question

You observe three carts moving to the right. cart a moves to the right at nearly constant speed. cart b moves to the right, gradually speeding up. cart c moves to the right, gradually slowing down. which cart or carts, if any, experience a net force to the right? (select all that apply.)

Answer 1

The cart with speed increasing to the right ... cart-b ... 
has a net force to the right acting on it. 

The others ...

... Cart-a has no net force at all acting on it, so its speed isn't changing.

... Cart-c has a net force toward the left acting on it, so its speed 
toward the left is INcreasing.  (That's the same thing as its speed
toward the right DEcreasing.