![]() Why isn't the Wall Included in the System?īased upon the problem statement, our choice of system may seem odd. What is the time-averaged force exerted on the wall by the ball during the collision? The ball rebounds from the wall with the same speed, but now directed at an angle of 60° W of N. Part A: A wall running north to south is hit by a 0.50 kg ball moving with a velocity of 12 m/s at an angle of 60° E of N. ![]() Various example problems asking for the force exerted on a wall by objects colliding with it. None of the profiles in figure 2 are clearly sharper than a triangle, though the baseball or steel ball might possibly be. To get an average value less than half, you would need a profile that is sharper than a triangle (spending more time at low values). A profile with a rounded cap, like the one for the tennis ball, spends more of its time near the peak than a triangle would. Thus, the average force for a triangular profile is 1/2 the height, and the height is simply the peak force. time curve and dividing by the time (the base of the triangle in this case). The average force is found by taking the area under the force vs. The reason is that a triangle has an area equal to the base times 1/2 the height. Can you explain why by looking at the shape of the profile?Įxplanation: What profile gives an average value equal to exactly half the peak value?Ī perfectly triangular force profile would give an average force of exactly half the peak value. The average force in this case is more than half of the peak value. Looking at the graph shows that the peak force on the tennis ball is between 80 and 85 N. If we define a y-axis pointing upward, then we can find the average force exerted on the tennis ball in the y-direction during the collision by using:īased upon the data in the graph, we approximate the duration of the collision ( t f - t i) to be approximately 5.75 ms. In the table, v 1 is the tennis ball's speed just before the collision (it is traveling downward) and v 2 is the tennis ball's speed just after the collision (it is traveling upward). Using the collision data provided in the table, we can compute the time-averaged force experienced by the tennis ball and compare it with the force profile. They have asymmetries.Ĭomparison of force profile with time-averaged force. They are certainly not flat horizontal lines (which would indicate constant force).
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