Question

1. If you drop a rock from a height of 21 meters, how fast is the rock moving when it hits the ground?? Hint 60

2. You launch a steel ball from the ground at 30 m/s upwards. Taking up to be the positive Find the speed of the steel ball after 3.5 seconds. Hint 61

3. If an arrow launched straight up at a speed of 300 feet/second at what speed will the arrow hit the ground if you ignore air resistance? Hint 59

4. If you jump straight out off a bride into the water and it takes 2.5 seconds to hit the water how high is the bridge. Hint 54

5. While cliff diving you step off a cliff 15 meters up. What is your speed when you hit the water? Hint 51

Answer 1

1) 20.49 ms⁻¹

2) ↓5 ms⁻¹ or -5 ms⁻¹

3) 300 ft/s

4)31.25 m

5) 17.32 ms⁻¹

Step-by-step explanation:

1)v² = u² + 2as

v² = 0 + 2g(21)

v = 20.49 ms⁻¹

u = 0 as the object is dropped. let g = 10 ms⁻²

2)a = (v-u)/t ⇒↑ v = u + at (a = g)

= 30 - 10×3.5 = ↓5 ms⁻¹ or -5 ms⁻¹

3) By the conservation of Energy principle,

Energy of the arrow just after launch = energy of the arrow just before hit ground

`(1)/(2) mu^(2)  = (1)/(2) mv^(2)\\v = u`

So velocity just before hitting ground is 300 ft/s

4) s = ut + (1/2)at²

= 0 + 0.5×10×(2.5)² = 31.25 m

5)v² = u² + 2as

v² = 0 + 2g(15)

v = 17.32 ms⁻¹