# Projectile motion problem

## Homework Statement

A m=77.39 kg person on a bike is riding at v0,b=11.83 m/s. Suddenly, he sees a child running across his path! He applies the brakes that provide a deceleration of a= -4.192 m/s2. His glasses were not attached properly to his face, so they fly away and land on the pavement. If the glasses are assumed to start their flight travelling horizontally at a height of h=1.354 m above the ground, how far will those glasses be from the place where the bicyclist stops? Express your answer as a displacement in metres from the bike so that if glasses are behind the bike, the distance is negative, and if the glasses are head, the distance is positive.

## Homework Equations

v=d/t
y=y0 +v0yt+1/2at^2
x=x0+v0xt+1/2at^2

collinsmark
Homework Helper
Gold Member

## Homework Statement

A m=77.39 kg person on a bike is riding at v0,b=11.83 m/s. Suddenly, he sees a child running across his path! He applies the brakes that provide a deceleration of a= -4.192 m/s2. His glasses were not attached properly to his face, so they fly away and land on the pavement. If the glasses are assumed to start their flight travelling horizontally at a height of h=1.354 m above the ground, how far will those glasses be from the place where the bicyclist stops? Express your answer as a displacement in metres from the bike so that if glasses are behind the bike, the distance is negative, and if the glasses are head, the distance is positive.

## Homework Equations

v=d/t
y=y0 +v0yt+1/2at^2
x=x0+v0xt+1/2at^2

## The Attempt at a Solution

Hello @Jpyhsics,

Welcome to PF!

In the future, please type out your work rather than link to an image of it. Images are fine for charts, graphs, and any supplemental material, but per the forum rules, we like to have it actually typed into the original post. (It's fine to do both, by the way, if that adds clarity.)

Anyway, your calculations involving the glasses look good to me. But your formula for the bicycle has a mistake in it. It's missing a t in there somewhere, leading to an incorrect answer.

(Also, for what it's worth, you might want to think about using a different kinematics formula for your bicycle calculation. It will save you a step. )

Hello @Jpyhsics,

Welcome to PF!

In the future, please type out your work rather than link to an image of it. Images are fine for charts, graphs, and any supplemental material, but per the forum rules, we like to have it actually typed into the original post. (It's fine to do both, by the way, if that adds clarity.)

Anyway, your calculations involving the glasses look good to me. But your formula for the bicycle has a mistake in it. It's missing a t in there somewhere, leading to an incorrect answer.

(Also, for what it's worth, you might want to think about using a different kinematics formula for your bicycle calculation. It will save you a step. )

Thank you so much!!

collinsmark