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Home Minds On Newton's Laws Mission NL5 Force Diagrams Help Help 6

Mission NL5 Force Diagrams

The Question

The diagrams below represent forces acting on an object. The size of the arrow represents the magnitude of the force. Which would be most consistent for the following scenario?
 
A rightward moving car is skidding to a stop; the wheels of the car are locked.

Game Plan

Often times, success in physics demands that you have the proper approach - a good game plan. A good game plan for this question would be to:
 
  • First, identify if the forces are balanced or unbalanced; and if unbalanced, determine the direction of the unbalanced force (see Think About It section below). This will allow you to eliminate several choices from among the ten diagrams.
  • Second, use your understanding of the various force types to determine if there is a force in each direction - up, down, right, left. This requires that you have a good understanding of the different types of forces and when they are present and absent (use the link in the Hot Link section if necessary). This second step allows you to reduce the number of choices to one.

Don't be Fooled

A common misconception among physics students is the belief that a rightward moving object must be experiencing a rightward force. But don't be fooled. If an object is moving to the right and speeding up then there must be more right force than left force acting upon it. If an object is moving to the right and slowing down then there must be more left force than right force acting upon it. And if an object is moving to the right with a constant speed then there must be the same amount of right force as left force acting upon it (if present at all).

A Very Fine Detail

A physics question often contains a short phrase that might seem a bit peculiar but serves to provide a hint or clue that might steer you in the right direction. In this question, the clue is in the phrase "the wheels of the car are locked." Including this phrase in the question warns the student that there is no forward propulsion force on the car that would result from the engine causing the wheels to turn. Thus, do not select a diagram with a rightward force.

Hot Link