You observe three carts moving to the left. cart a moves to the left at nearly constant speed. cart b moves to the left, gradually speeding up. cart c moves to the left, gradually slowing down. which cart or carts, if any, experience a net force to the left? cart a cart c cart b

cart B

Explanation:

For cart A speed is constant therefore there is no acceleration because acceleration is rate of change of velocity

thus there is no net force

For cart B there is change in velocity in the left direction , so there is net acceleration towards left

so there is net force in the left direction

For cart C there is decrease in velocity i.e. negative acceleration or deceleration . Therefore there is a net force towards right which opposes the motion                

none, its a machine