Problem 10E

10. A particle moves with position function

$$

s=t^{4}-4 t^{3}-20 t^{2}+20 t \quad t \geqslant 0

$$

(a) At what time does the particle have a velocity of $20 \mathrm{~m} / \mathrm{s} ?$

(b) At what time is the acceleration $0 ?$ What is the significance of this value of $t$ ?

 

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