Solving Elastic Collision Homework: Average Force on a 100g Ball

[slanderson113]

Homework Statement

A 100 g ball bounces off a wall elastically. Its initial speed is 3 m/s perpendicular to the wall. If the collision lasts for 10 ms, what is the average force exerted by the wall on the ball?

Homework Equations

F=ma
Conservation of energy & momentum (?)
F=dP/dt

The Attempt at a Solution

I know to find average force the equation is m(vf-vi)/change in time. And in the equation were given the mass, time, and initial velocity, but to finish I need the final velocity but the conservation of energy and momentum, shows it should be the same as the initial making the force zero, however that's not one of the options. Please help!

 

[tiny-tim]

welcome to pf!

hi slanderson113! welcome to pf!

… the conservation of energy and momentum, shows it should be the same as the initial …

no, momentum is a vector, and it'll be opposite

 

[Doc Al]

And in the equation were given the mass, time, and initial velocity, but to finish I need the final velocity but the conservation of energy and momentum, shows it should be the same as the initial making the force zero, however that's not one of the options. Please help!

Realize that velocity is a vector and thus direction matters. The direction of the velocity is represented by its sign. (Do you still think that the initial and final velocities are the same?)

 

[slanderson113]

Oh my gosh thank you guys so much!