Dynamics: Why a Yo-Yo Falls Slower Than a Stone
Motion, forces, energy and momentum for particles and spinning bodies, from braking distances and airbags to figure skaters and engine linkages.
Dynamics · 50 questions
Try 3 questions
1. A ball thrown straight up reaches its highest point. What is its acceleration at that instant?
- About 9.8 m/s² upward
- About 9.8 m/s² downward
- Zero, since it has stopped
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Answer: About 9.8 m/s² downward
Velocity is momentarily zero, but gravity never switches off, so the acceleration stays g downward the whole flight.
2. Ignoring air resistance, which launch angle gives a projectile the longest range on level ground?
- 30 degrees
- 45 degrees
- 60 degrees
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Answer: 45 degrees
Range is v² sin(2θ)/g, which peaks when 2θ = 90°. Real balls with drag do best somewhat lower.
3. Two balls leave the ground at the same speed, one at 30° and one at 60°. Ignoring air, how do their ranges compare?
- The 30° ball goes twice as far
- They land at the same distance
- The 60° ball goes twice as far
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Answer: They land at the same distance
sin(60°) = sin(120°), so complementary angles give equal ranges; the 60° ball just flies higher and longer.
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