# Momentum - Height

## Homework Statement

A stone of mass 'm' is dropped from rest at a height of 1.98 m. From what height would a stone of mass 'm/2' have to be dropped to have the same momentum upon striking the ground?

?

## The Attempt at a Solution

i don't understand 'm/2' doesn't this mean the first mass divided by 2 and so could i not just simple divide1.98 by 2?

this is probably the simplest question on this assignment and i don't get it PhanthomJay
Homework Helper
Gold Member

## Homework Statement

A stone of mass 'm' is dropped from rest at a height of 1.98 m. From what height would a stone of mass 'm/2' have to be dropped to have the same momentum upon striking the ground?

?

## The Attempt at a Solution

i don't understand 'm/2' doesn't this mean the first mass divided by 2 and so could i not just simple divide1.98 by 2?
No. The second mass has half the mass of the first mass. What is the momentum of the first ? You'll need to find its speed.Then proceed to work on the momentum of the second mass.

how do i do that though if i don't have any number for mass the only number i have is the height of 1.98 m i wasnot given any other numbers?

PhanthomJay
Homework Helper
Gold Member
how do i do that though if i don't have any number for mass the only number i have is the height of 1.98 m i wasnot given any other numbers?
use m for the mass of mass1, and use m/2 for the mass of mass 2. That will work. Now you have a distance but not a speed. Use one of your motion eqautions from kinematics that solves for the speed as a function of the height. Are you familiar with these equations?

ok can i use the formula v=square root of 2(9.8)(1.98) ?
and then i need to solve for the mass but i don't recall an equation i can use to find mass since i don't have momentum

by the way, if one rock has half the mass of the other, how should its speed relate to the other to have the same momentum?

i was thinking that its speed would be less because it is lighter?

PhanthomJay