A toy rocket is launched vertically from ground level at time t = 0.00 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 81 m and acquired an upward velocity of $ 40 \mathrm{~m} / \mathrm{s} $ The rocket continues to rise with insignificant air resistance in unpowered flight, reaches maximum height, and falls back to the ground. The upward acceleration of the rocket during the burn phase is closest to
A) 9.9 m/ $ \mathrm{s}^{2} $.
B) 9.6 m/ $ \mathrm{s}^{2} $ .
C) 9.3 m/ $ \mathrm{s}^{2} $ .
D) 9.0 m/ $ \mathrm{s}^{2} $ .
E) 8.7 m/ $ \mathrm{s}^{2} $ .

Question

Quizplus · Accepted Answer

Using the kinematic equation $ v^2 = u^2 + 2as $, where $ v = 40 \, \mathrm{m/s} $, $ u = 0 \, \mathrm{m/s} $, and $ s = 81 \, \mathrm{m} $, we solve for $ a $: $ 40^2 = 0 + 2a \times 81 $. Solving gives $ a \approx 9.9 \, \mathrm{m/s}^2 $.

A Toy Rocket Is Launched Vertically from Ground Level at Time