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## Homework Statement

an object with m=100kg is moving on a straight line. for t=0 its speed is v0=20 m/s. There's a force which is opposing to the movement F=C*v^2 ( C=1kg/m and v is the speed (v(t)=...) ). Find the time t1 in which the speed v=v0/2.

## Homework Equations

F=m*a (?)

v(t)=a*t+v0

## The Attempt at a Solution

v1=a*t1+v0 --> v0/2=a*t1+v0 --> t1=(-v0/2)*1/a

assuming a (accelation) constant

m*a = F = C*v1^2= C*(v0/2)^2

a= [C*(v0/2)^2]/m

Putting a in

t1= (-v0/2)/a should be getting the answer

Unfortunately the answer I get is not correct (should be 5second)