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A crash test car of mass 1000kg moving at constant speed of 12m/s collides completely inelastically with an object of mass M at time t=0. the object was initially at rest. the speed v in m/s of the car-object system after the collision is given as a function of time t in seconds by the expression

v=8/(1+5t)

(a)calculate the mass of the object

(b) assuming the initial position of x=0, determine an expression for the car object system after the collision as a function of time t

(c)determine an expression for the resisting force on the car-object system after the collision as a function of time t.

(d) determine the impulse delivered to the car-object system from t=0 to t=2s

I am currently doing A, and I came up with:

m1v1=(m1+m2)v2 <= (law of conservation)

(1,000)(12)=(1000+M)8

I got the 8 by plugging t=0 into v=8/(1+5t)

so M=1400KG? For some reason it does not seem right ...