Final answer:
It takes 0 seconds for the rock to hit the ground.
Step-by-step explanation:
To calculate the time it takes for the rock to hit the ground, we can use the formula h(t) = -4.9t² + v₀t + h₀, where h(t) represents the height of the rock at time t, v₀ is the initial velocity, and h₀ is the initial height. In this case, the initial height is 70 meters, and since the rock is dropped, the initial velocity is 0. Plugging in these values, we get the equation 70 = -4.9t² + 0t + 70. Solving this equation will give us the value of t, which represents the time it takes for the rock to hit the ground.
Using this equation, we can simplify it to 70 = -4.9t² + 70. By rearranging the equation and removing the constant term, we get -4.9t² = 0. Simplifying further, we have t² = 0. Dividing both sides by -4.9 gives us t² = 0 / -4.9, which simplifies to t² = 0. We can take the square root of both sides, giving us t = 0. Therefore, it takes 0 seconds for the rock to hit the ground.