How High Is the Bridge Based on Projectile Motion?

  • Thread starter Thread starter keithcuda
  • Start date Start date
  • Tags Tags
    Bridge
Click For Summary
SUMMARY

The problem involves calculating the height of a bridge based on the horizontal distance a rock travels when thrown horizontally. Given that the rock hits the water 30 meters away and is in the air for 2 seconds, the correct formula to use is d = 0.5 * g * t², where g is the acceleration due to gravity (9.8 m/s²). The calculation yields a height of 19.6 meters for the bridge, confirming that the initial assumption was correct. The confusion arises from misinterpreting the distance traveled in the first second versus the speed at that moment.

PREREQUISITES
  • Understanding of projectile motion principles
  • Familiarity with the equations of motion, specifically d = 0.5 * g * t²
  • Knowledge of gravitational acceleration (9.8 m/s²)
  • Basic algebra for solving equations
NEXT STEPS
  • Study the concepts of vertical and horizontal motion in projectile motion
  • Learn about the effects of air resistance on projectile trajectories
  • Explore advanced projectile motion problems involving angles
  • Investigate real-world applications of projectile motion in physics
USEFUL FOR

Students studying physics, educators teaching projectile motion, and anyone interested in understanding the dynamics of objects in motion.

keithcuda
Messages
43
Reaction score
0

Homework Statement


A rock thrown horizontally from a bridge hits the water below 30 meters away in the horizontal direction. If the rock was in the air for 2 seconds, how tall is the bridge?

Homework Equations


d=.5gt2

The Attempt at a Solution


I think I am going about this the right way. Just want to double check.

d=.5*9.81*4
d= 19.62m
The bridge would be 19.62m high?

cheers,
Keith
 
Physics news on Phys.org
It's been about 50 years since I've actually worked out a problem like that but it sounds wrong, and here's why: the acceleration due to gravity is 9.8 meters per second per second. That means that the rock will travel 9.8 meters in the first second, but much more in the next second, so the total can't be 9.8 x 2 which is what you got.
 
phinds said:
It's been about 50 years since I've actually worked out a problem like that but it sounds wrong, and here's why: the acceleration due to gravity is 9.8 meters per second per second. That means that the rock will travel 9.8 meters in the first second, but much more in the next second, so the total can't be 9.8 x 2 which is what you got.
It looks right to me. The first second it travels ~ 5 m, and the second second, it travels ~15 m.

Chet
 
  • Like
Likes keithcuda
Chestermiller said:
It looks right to me. The first second it travels ~ 5 m, and the second second, it travels ~15 m.

Chet
Guess I have it wrong then that it travels 9.8m in the first second. I guess what the figure means is that at the end of the first second it is MOVING at 9.8 m/s, not that it has MOVED 9.8 m ... 50 years ago I bet I would have got it right :oldtongue:
 

Thread 'Magnitude of buoyant force in fluids of different densities'

The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?
View full post »

Similar threads

How do I find the final velocity and how high the bridge is?
  • · Replies 2 ·
Replies
2
Views
2K
A stone is thrown off a bridge....
  • · Replies 4 ·
Replies
4
Views
2K
How do I calculate the height of a bridge using one dimension?
  • · Replies 7 ·
Replies
7
Views
2K
2D Kinematics - 2 rocks off a bridge
  • · Replies 1 ·
Replies
1
Views
3K
Projectile Motion: Angle of Impact
  • · Replies 2 ·
Replies
2
Views
18K
I need opinions on a Projectile Motion problem that I made up
  • · Replies 11 ·
Replies
11
Views
2K
1-D Projectile Motion: Throwing a Rock
  • · Replies 5 ·
Replies
5
Views
7K
Calculating Projectile Distance on Pluto
  • · Replies 13 ·
Replies
13
Views
2K
Problem Set Involving Inertia and Balloons
  • · Replies 2 ·
Replies
2
Views
2K
How to calculate projectile off cliff when angle is below th
  • · Replies 3 ·
Replies
3
Views
2K