s(t)=[(9t)i + (-2t^2)j] meters A) What is the magnitude and direction of the mou

Question

s(t)=[(9t)i + (-2t^2)j] meters A) What is the magnitude and direction of the mouse'snet displacement at the end of 2 seconds? B) What is the magnitude and direction of the mouse'sinstantaneous velocity at 2 seconds? C) What is the magnitude and direction of the mouse'sacceleration at t=2 seconds? D) What is the magnitude of the force on the mouse att=2 seconds? Is the force constant? How do youknow?
My answers: A) plugging in 2 for t and solving for displacement s(t)= [9(2)i + -2(2^2)j] m 18i+(-8j) 18i-8j m at tan^-1 (-8/18) =-24 degrees R=19.7m
plugging in 2sec for t and solving for instantaneousvelocity 9i-4(2)j 9i-9j
C) I need help with acceleration. Isn't accelerationjust instantaneous velocity?
D) F=ma what's acceleration

Explanation / Answer

(c)    s(t)=[(9t)i + (-2t^2)j] meters    velocity, V = ds / dt = ( 9 i - 4t j )m/s    acceleration, a = dv / dt = - 4 j m/s^2    magnitude of acceleration, a = 4 m/s^2                         direction of a = -ve y-axis (d)    mass, m = 30 kg    Force , F = ma =30 * - 4 j = - 120 j N    Here Force is constant , because it isindependent of 't'       magnitude of force, F =120 N             directionof F = -vey-axis        

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