<p>Heather and Jerry are standing on a bridge 47 &#160;above a river. Heather th

Question

<p>Heather and Jerry are standing on a bridge 47 &#160;above a river. Heather throws a rock straight down with a speed of 20 . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance.</p>

Explanation / Answer

(A) How much time elapses between the first splash and the second splash?? (B)Which rock has the faster speed as it hits the water? (A) 1st rock:- =>By s = ut + 1/2gt^2 =>50 = 20t + 1/2 x 9.8 x t^2 =>4.9t^2 + 20t - 50 = 0 =>t = [-20+/-v{(20)^2 - 4 x 4.9 x (-50)}]/[2 x 4.9] =>t = [-20+/-37.15]/9.8 =>t = 1.75 sec 2nd rock:- =>=>By s = ut + 1/2gt^2 =>50 = -20t + 1/2 x 9.8 x t^2 =>4.9t^2 - 20t - 50 = 0 =>t = [-(-20)+/-v{(-20)^2 - 4 x 4.9 x (-50)}]/[2 x 4.9] =>t = [20+/-37.15]/9.8 =>t = 5.83 sec Thus ?t = t2 - t1 =>?t = 5.83 - 1.75 = 4.08 sec (B) Both will strike with the same speed =>As by the law of energy conservation:- =>[PE + KE]initial = KE(final)

Related Questions

Navigate

• Browse (All)
• Browse #
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.