A test rocket is fired straight up from rest with a net acceleration of 20 m/s².After 4 seconds the motor turns off,but the rocket continues to coast upward.What maximum elevation does the rocket reach? A)487 m B)327 m C)320 m D)408 m E)160 m

Question

Quizplus · Accepted Answer

Explanation:The rocket reaches its maximum elevation when its velocity is zero. We can use the equation of motion:v = u + atwhere v is the final velocity, u is the initial velocity, a is the acceleration, and t is the time.At the maximum elevation, v = 0, so we have:0 = u + at-u = att = -u/aWe know that the initial velocity is 0, so we have:t = 0This means that the rocket reaches its maximum elevation at the instant the motor turns off.We can now use the equation of motion:s = ut + 1/2 at^2where s is the displacement, u is the initial velocity, a is the acceleration, and t is the time.At the maximum elevation, s is the maximum elevation, u is 0, and t is 4 seconds, so we have:s = 1/2 * a * t^2s = 1/2 * 20 m/s^2 * (4 s)^2s = 160 mTherefore, the maximum elevation is 160 m.

A Test Rocket Is Fired Straight Up from Rest with a Net