How High Does a 64 lb Projectile Go When Fired Upward at 2000 ft/sec?

[anik18]

A projectile weighing 64 lb is fired directly upward with a velocity 2000 ft/sec. Assume that the accerleration due to gravity is constant, and the air resists the motion with a force proportional to the velocity. When the velocity is 1000 ft/sec, the resisting force is 20 lb. Find the maximum height attained by the projectile, and the time required for it to reach this height.

please help this.
thankyou

 

[D H]

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