Positive (Upward) Launch Video Lessons

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Problem: A javelin thrower standing at rest holds the center of the javelin behind her head, then accelerates it through a distance of 70 cm as she throws. She releases the javelin 2.0 m above the ground traveling at an angle of 30 above the horizontal. Top-rated javelin throwers do throw at about a 30° angle, not the 45 ^circ you might have expected because the biomechanics of the arm allows them to throw the javelin much faster at 30 ^circ than they would be able to at 45. In this throw, the javelin hits the ground 63 m away.What was the acceleration of the javelin during the throw? Assume that it has a constant acceleration.

FREE Expert Solution

In this problem, we are launching a projectile upward at an angle. We have two parts: the first 70cm and the projectile part. The target lies in the 70cm motion. 

Let's restate the UAM equations:

 vf = v0 +atx= (vf+v02)tx= v0t+12at2 vf2= v02 +2ax

 vf = v0 -gty= (vf+v02)ty= v0t-12gt2 vf2= v02 -2gy

Let's organize information for the target part (70cm):

  • x = 0.70m
  • a = ? (target)
  • v0 = 0 m/s
  • t = ?
  • vf = ?
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Problem Details

A javelin thrower standing at rest holds the center of the javelin behind her head, then accelerates it through a distance of 70 cm as she throws. She releases the javelin 2.0 m above the ground traveling at an angle of 30 above the horizontal. Top-rated javelin throwers do throw at about a 30° angle, not the 45 you might have expected because the biomechanics of the arm allows them to throw the javelin much faster at 30 than they would be able to at 45. In this throw, the javelin hits the ground 63 m away.

What was the acceleration of the javelin during the throw? Assume that it has a constant acceleration.

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Based on our data, we think this problem is relevant for Professor Coutu's class at PSU.