# Momentum and impulse question # 2

an object #1 is motionless and has a mass 10 times greater than the mass of object #2. if object #2 has a velocity of 50.0 m/s before impacting object #1 and if the collision is inelastic determine the final velocity of the objects...

so i am confused do i mult. object #1 by 10 or object #2 i always get confused by 10 times greater than.. and how am i suppose to find velocity without given any masses?
i know i will use (m1v1 + m2v2) before collision = (m1v1 + m2v2) after collision. equation.. but wt do u plug in for m (mass) ?
i really need help..

cepheid
Staff Emeritus
Gold Member
so i am confused do i mult. object #1 by 10 or object #2 i always get confused by 10 times greater than..

This should clear that up:

object #1...has a mass...greater than...object #2.

This is a direct quote from your problem statement. All I did was remove some intermediate words and add boldface for emphasis.

so that means object #1 is 10 times greater than #2 so i mult object #1 by 10 right?

PeterO
Homework Helper
an object #1 is motionless and has a mass 10 times greater than the mass of object #2. if object #2 has a velocity of 50.0 m/s before impacting object #1 and if the collision is inelastic determine the final velocity of the objects...

so i am confused do i mult. object #1 by 10 or object #2 i always get confused by 10 times greater than.. and how am i suppose to find velocity without given any masses?
i know i will use (m1v1 + m2v2) before collision = (m1v1 + m2v2) after collision. equation.. but wt do u plug in for m (mass) ?
i really need help..

Generally in a problem, if the answer is affected by the ACTUAL mass, you will be told that mass. If you are told, the ACTUAL mass will not make any difference to the final answer sought.

SO ... let object 1 have a mass of 2kg, and thus object 2 have mass 20 kg and see what you get.
If you suspect you shouldn't do that, repeat the problem with masses of 6kg and 60kg to check the final answer is the same.

cepheid
Staff Emeritus
Gold Member
so that means object #1 is 10 times greater than #2
Yes

so i mult object #1 by 10 right?

No.

If object 1 is 10 times more massive than object 2, then this means you need to take the mass of object 2 (the lighter one) and multiply it by 10 in order to get the mass of object 1 (the heavier one). It's all there in the wording:

"mass 1 is ten times mass 2"

m1 = 10 x m2

so it will be like this m1v1 + m2v2 = m1v1 + m2v2
1m(0)+ 10m(5om/s) = 11m (v) ??
v= 45.4 m/s ?/?

cepheid
Staff Emeritus