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equation of motion of a projectile shot upward Consider a projectile of mass m w

ID: 1891849 • Letter: E

Question

equation of motion of a projectile shot upward Consider a projectile of mass m which is shot vertically upward from the surface of the earth with initial velocity V. Assume that the gravitational force acts downward at a constant acceleration g while the force of air resistance has a magnitude proportional to the square of the velocity with proportionality constant k>0 and acts to resist motion. Let x=x(t) denote the height of the projectile at time t and v(t) = dx/dt(t) , its velocity. a) Explain why the governing equation of motion is given by: mdv/dt = -kv^2 - mg v > 0 For t > 0 (1) mdv/dt = kv^2 - mg v < 0 x(0) = 0 and v(0) = Vo b) Solve this system as follows: Introduce V(x) = v[t(x)]. Then define V1(x) = V^2(x) for V(x) >0 and V2(x) = V^2(x) for V(x) < 0. Show that V1 and V2 satisfy dV1/dx + 2k/m V1 = -2g , V1(0) = Vo^2 dV2/dx - 2k/m V1 = -2g , V2(Xm) = 0 Where Xm is defined implicitly by V1(Xm) = 0. Demonstrate that V2(0) < Vo^2.

Explanation / Answer

the eqution of motion for the upward motion is