Learning Goal: To apply Problem Solving Strategy 4.1 Newton's laws.. The froghopper (Philaenus spumarius), the champion leaper of the insect world, has a mass of 12.3 mg. It can leave the ground with a speed as high as 4.0 m/s in the vertical direction. The jump itself lasts a mere 1.0 ms before the insect is clear of the ground. Assuming constant acceleration, find the force that the ground exerts on the froghopper during its jump. Problem-Solving Strategy 4.1 Newton's laws SET UP 1. Define your coordinate system. Be sure to draw a diagram showing the positive axis direction. If you know the direction of the acceleration, it's often convenient to take that as your positive direction. If you need to calculate displacements of the moving object, specify the location of the origin of your coordinate system. 2. Be consistent with signs. Once you define the x axis and its positive direction, the components of velocity, acceleration, and force in that direction are also positive. 3. Concentrate on a specific object. Draw a free-body diagram showing all the forces (magnitudes and directions) acting on this object, but do not include forces that the object exerts on any other object. Represent the object as a dot or by a simple sketch. SOLVE 4. Identify the known and unknown quantities, and give each unknown quantity an algebraic symbol. If you know the direction of a force at the start, use a symbol to represent the magnitude of the force. 5. Always check units for consistency. REFLECT 6. Check to make sure that your forces obey Newton's 3rd law. When you can guess the direction of the net force, make sure that its direction is the same as that of the acceleration, as required by Newton's 2nd law. SET UP Before writing any equations, organize your information and draw appropriate diagrams. Part A It is easiest to choose your coordinate system so that the acceleration of the object of interest is in the positive direction. In which direction does the froghopper accelerate? upward downward to the left to the right Submit Previous Answers Correct Now that you've figured out which direction it accelerates, you should draw your coordinate system with the positive y axis pointing upward. Part B Since you are concerned with the froghopper's acceleration, you need to draw a free-body diagram for the froghopper. Which of the following forces should be included on your free-body diagram? The normal force n₁ exerted by the froghopper on the ground The normal force 72 exerted by the ground on the froghopper The weight w of the froghopper 71 only 72 only 7₁ and w only П2 and w only 71 and 72 only 71, 72, and w Submit Previous Answers Part C Correct Before you answer the next part, you should draw your free-body diagram for the froghopper. In Part A, you defined the coordinate system to have the positive y direction pointing upward. Give the directions of the normal force n exerted by the ground on the froghopper and the froghopper's weight w using this coordinate system. Give the direction of the normal force followed by the direction of the weight separated by a comma. For instance, if you thought that both were directed downward, you would enter -,-. Submit Previous Answers Request Answer × Incorrect; Try Again