[ALI ALZAHRANI]

المشاركة الأصلية كتبت بواسطة ROoOFaNA a) if aprticle,s position is ginen by x=4-12t+3t^2 (where t is in second and x is in meter) , what is its velocity at t=1s? b) isit moving in the positive or negative direction of x just then? c)what is its speed just then? d) is the speed increasing or decreasing just then? e) is there ever an instant when the velocity is zero?if so .give the if not answer no. f)is there atime after t=3s when the particle is moving in the negative direction of x? if ,so give the time t : if not answer no. sol. Velocity at 1s= v=dv/dt=0-12+6t=-12+6t a) Vat 1s=-12+6.1=-6m/s CORRECT b) in the negative CORRECT but HOW?! v is negative at t=1, then its moving in the negative direction c)?? speed is the magnitude of the velocity s=|v| =|-6| = 6 m/s d)? v= -12 +6t at t=0, v= -12 m/s ====> s=12 m/s at t=1, v= -6 m/s ====> s=6 m/s at t=2, v= 0 m/s ====> s=0 m/s at t=3, v= 6 m/s ====> s=6 m/s at t=4, v= 6 m/s ====> s=12 m/s and so on form [0,2], speed decreases from (2,infinity], speed increases e)v=0 t=2s v=-12+6t 0=-12+6t T=2 CORRECT f)? No, as we have done in part d The following equation give the position x of a particle in four situation a)x=3t-4 v=dx/dt =3 b)x=-5t^3+4t^2+6 v=-15t^2+8t c)x=2/t^2-4/t v=4t^3-4t^2 d)x=5t^2-3 v=10t CORRECT if the question is to find the velocity at any time.

Take care Ro