A girl drops a rock from the edge of a cliff and observes that it strikes the bo

Question

A girl drops a rock from the edge of a cliff and observes that it strikes the bottom 6.00 s later. How high is the cliff? A ball thrown vertically upward has an upward velocity of 8.00 m/s at a point 20.0 m above where it was thrown. How long does the ball take to reach that point? And what maximum height the ball can reach? The brakes are applied to a car traveling on a dry, level highway. A typical value for the magnitude of the car's acceleration is 2.50 m/s^2. If the car's initial speed is 60.0 m/s, how far does it travel, starting from the moment the brakes are applied?

Explanation / Answer

3. S = ut + 0.5g*t^2

=> 20 = 0 + 0.5 * 10 * 36

    S = 180m

4. v^2 - u^2 = -2gS

   => 64 - u^2 = -2 * 10 * 20

         u = sqrt(464) = 21.54m/s

    t = (v-u)/-g

    t = (8-21.54)/10 = 1.354 sec

    max height attained when v = 0

     => -464 = -2 * 10 * S

        S = 23.2m

5.

v^2 - u^2 = -2aS

=>-3600 = -2 * 2.5 * S

=> S = 720m

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

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