A projectile of mass 0.750 kg is shot straight up with an initial speed of 18.0 m/s. How high would it reach with no air resistance? What is the average force of the air exerted on it if the projectile reaches a max height of 11.8 with air resistance?

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Answer 1 · 2017-06-03T17:01:52

The force of the air resistance is #=2.95N#

The loss in kinetic energy is #=# the gain in potential energy

#Delta KE=PE#

#1/2m u^2-1/2mv^2=mgh#

The initial velocity is #u=18ms^-1#

The final velocity is #v=0ms^-1#

The height is #=hm#

#1/2m u^2-0=mgh#

#h=u^2/(2g)=18^2/(2g)=16.53m#

There is a loss of potential energy due to air resistance

#Delta PE=mg(h-11.8)#

This is equal to the work done by the force of air resistance

#0.750*9.8(16.53-11.8)=R*11.8#

The force of the air resistance is #R=(0.750*9.8*4.73)/11.8=2.95N#