an object is shot straight upward from sea level with an initial velocity of 250 ft/sec.
a)assuming that gravity is the only force acting on the object, give an upper estimate for it's velocity after 5 seconds has elapsed. use g=32 ft/sec^2 for gravitational acceleration.
b) using delta t=1 sec, find a lower estimate for the height attained after 5 seconds.

Question

an object is shot straight upward from sea level with an initial velocity of 250 ft/sec.  
a)assuming that gravity is the only force acting on the object, give an upper estimate for it's velocity after 5 seconds has elapsed.  use g=32 ft/sec^2 for gravitational acceleration.  
b) using delta t=1 sec, find a lower estimate for the height attained after 5 seconds.

anonymous · Answer

For part a you would need the equation $$Vf = Vi + a \Delta t$$

For part b you would use the equation $$\Delta x = Vi \Delta t + 1/2 a \Delta t ^{?}$$

anonymous · Answer

so for part a do i get 410

anonymous · Answer

Almost, we need to be careful of direction.  Remember the gravitational force acts downward while the initial velocity is directed upward.  We represent the two different directions by changing the sign.  So, for example you would use -32 ft/sec^2 in the equation to represent the acceleration being downward.

Also, we expect that it should be slowing down as it travels upward.  So a larger velocity of 410 ft/sec should be a red flag. :)

anonymous · Answer

okay....so i received an answer of 90 for a....im sorry im just not feeling very confident with this.

anonymous · Answer

No worries.  It takes practice.  Yes 90 ft/sec directed upward is the velocity after 5 seconds.