Calculating the Velocity and Time of a Freely Falling Rock

In summary, a small rock is thrown vertically upward from the edge of a 30.0-m-tall building with an initial speed of 18 m/s. The rock does not hit the building on its way back down and lands in the street below. Air resistance is neglected. To find the speed and time when the rock hits the street, the equations 0=30+18t-4.9t^2 and Vx=30-9.8t are used. From these equations, the speed of the rock just before it hits the street is -66.04 m/s and the time elapsed from when the rock is thrown until it hits the street is 9.8 seconds. However, the initial velocity was
  • #1
ThiagoG
15
0

Homework Statement


A small rock is thrown vertically upward with a speed of
from the edge of the roof of a 30.0-m-tall building. The
rock doesn’t hit the building on its way back down and lands in the
street below. Air resistance can be neglected. (a) What is the speed
of the rock just before it hits the street? (b) How much time elapses
from when the rock is thrown until it hits the street?


Homework Equations


0=30+18t-4.9t2
Vx=30-9.8t


The Attempt at a Solution


For the time I got 9.8s and for the velocity I got -66.04 m/s. I'm not sure where I went wrong.
 
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  • #2
You didn't provide the initial velocity.
 
  • #3
Lamebert said:
You didn't provide the initial velocity.

Sorry about that. The initial velocity is 18 m/s.
 

Related to Calculating the Velocity and Time of a Freely Falling Rock

What is a freely falling body?

A freely falling body is an object that is only affected by the force of gravity and is not experiencing any other forces such as air resistance or friction. It is essentially an object that is falling in a vacuum.

What is the acceleration of a freely falling body?

The acceleration of a freely falling body is always constant and equal to 9.8 meters per second squared (m/s²) near the Earth's surface. This acceleration is denoted by the symbol "g" and is the same for all objects, regardless of their mass.

What is the difference between free fall and free fall motion?

Free fall refers to the state of an object that is falling without any other forces acting upon it, while free fall motion refers to the path or trajectory that the object follows as it falls. In other words, free fall motion is the result of an object in free fall.

How does air resistance affect freely falling bodies?

Air resistance is a force that opposes the motion of an object through air. It can slow down the acceleration of a freely falling body and ultimately limit its maximum velocity. However, in a vacuum where there is no air resistance, all objects will fall with the same acceleration regardless of their mass.

What is the equation for calculating the distance traveled by a freely falling body?

The equation for calculating the distance traveled by a freely falling body is d = ½ * g * t², where d is the distance traveled, g is the acceleration due to gravity, and t is the time taken. This equation assumes that the object starts from rest and is only affected by the force of gravity.

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