# 2D Kinematics - 2 rocks off a bridge

• kenji1992
In summary, Heather and Jerry are standing on a bridge 60m above a river. Heather throws a rock straight down with a speed of 14m/s while Jerry throws a rock straight up with the same speed. They both experience the same acceleration of 9.8m/s^2. To determine the time between the first splash and the second splash, a kinematics equation can be used. Both rocks will have the same acceleration, but different initial velocities. The equation should contain the variables v0, g, t, y0, and y.
kenji1992
2D Kinematics -- 2 rocks off a bridge

## Homework Statement

Heather and Jerry are standing on a bridge 60m above a river. Heather throws a rock straight down with a speed of 14m/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance.

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?

## The Attempt at a Solution

H and J are 60 m above a river.
Heather throws the rock down with a speed, v=14 m/s
Jerry throws it up, v = 14 m/s

a. I'm assuming that I have to use some vertical/horizontal motion formula, but I don't know...
b. Don't they both have the same acceleration 9/8 m/s^2 so the same speed?

kenji1992 said:
a. I'm assuming that I have to use some vertical/horizontal motion formula, but I don't know...
b. Don't they both have the same acceleration 9/8 m/s^2 so the same speed?

You will not need to worry about horizontal motion.
You are right that they will both have the same acceleration, but they both have different initial velocities.

Look for a kinematics equation that has everything you need. It should have...
v0, g, t, y0, y

You have already identified v0, g. What are t, y0, and y?

## What is 2D Kinematics?

2D Kinematics is the branch of physics that deals with the motion of objects in a two-dimensional space. It involves studying the position, velocity, and acceleration of objects in both the x and y directions.

## What is the significance of 2 rocks off a bridge in 2D Kinematics?

This scenario is commonly used in physics problems to illustrate projectile motion in a 2D space. It allows us to apply the principles of 2D Kinematics to analyze the motion of objects in a more complex and realistic scenario.

## How do you calculate the initial velocity of the rocks?

The initial velocity of the rocks can be calculated using the equation v = d/t, where v is the velocity, d is the distance traveled, and t is the time it takes for the rocks to fall from the bridge to the ground. This assumes that the rocks are dropped from rest.

## What factors affect the motion of the rocks in this scenario?

The motion of the rocks is affected by factors such as the initial velocity, the angle of release, the force of gravity, air resistance, and the height of the bridge. These factors can impact the trajectory, speed, and final position of the rocks.

## Can 2D Kinematics be applied to real-life situations?

Yes, 2D Kinematics can be applied to real-life situations such as the motion of objects in sports, the trajectory of projectiles, and the movement of vehicles. It is a fundamental concept in physics that helps us understand and predict the motion of objects in a two-dimensional space.

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