Please Help!!! 3) An object with cross section A is shot horizontally across fri
ID: 2290698 • Letter: P
Question
Please Help!!! 3) An object with cross section A is shot horizontally across frictionless ice. Its initial velocity is vox at t0 = 0s. Air resistance is not negligible. a) Show that the velocity at time t is given by the expression b) A 16 m wide,1.4m high,1500 kg car hits a very slick patch of ice while going 20 m/s. If friction is neglected, how long will It take until the cars speed drops to 10m/s? To 5m/s? c) Assess whether or not it is reasonable to neglect kinetic friction-in other words, how would the force of kinetic friction between the tires and ice compare to the drag force?Explanation / Answer
a) in this problem law conservation of momuntum holds good
drg force=momentum of object
Fd=axvsxv0t
force on object Fa=mx(vf-vi)/t
vf=vs,vi=v0t
solve the equations get the answer
b) in this question treat car as particle use model for rolling friction
car experience rolling and drag force
actually drag is less than friction at low speeds
drag increases with speed
there is no motion and accelration in verticle direction
we need to resolve components in horizontal manner
so Fd=0.25xAxV2
frictional force is f=un
=umg
these two equations are in equillibrium
Fd=f
area of car=1.6x1.4
=2.24
take u=1 frictionless
substitute in equation
velocity is very high
vi=162m/s final velocity is given in part a question solve t by using these values in equation
c) in this question friction is neglected such that
sliding is very high
there is no opposing force to control the speed
drag force varies with respect to speed
kinetic friction must be greater