# How to calculate minimum speed a ball needs to be rolling to move up when hitting a wall? [closed]

A ball of mass $m$ is rolling on the floor without sliding towards a vertical wall. Friction coefficient between the ball and the wall is $u$ and standard gravity is $g$. Ball and the wall are perfectly elastic with an infinite elasticity coefficient and the collision is very short.

What is the minimal velocity of the ball necessary for the ball to "jump" as a result of the collision?

My way of thinking:
Because the collision lasts is "very short" the force acting perpendicular to the surface of the wall on the ball is very large. Thus so is the friction. Thus the inertia is transformed into vertical motion. This would mean no matter the speed the ball would move up. This doesn't seem to be a correct answer though.

How to correctly calculate the velocity necessary given only the data in the text? Why is my approach incorrect?

## closed as off-topic by John Rennie, user36790, Jon Custer, rob♦, ACuriousMind♦Oct 7 '16 at 22:26

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – John Rennie, Community, Jon Custer, rob, ACuriousMind
If this question can be reworded to fit the rules in the help center, please edit the question.

• Hi and welcome to the Physics SE! Please note that this is not a homework help site. Please see this Meta post on asking homework questions and this Meta post for "check my work" problems. – John Rennie Oct 7 '16 at 9:19
• I know this is not a homework help site and I read the meta-post. This question seemed similar to the "Good" examples because I went to know the approach necessary, not the exact answer. – TTkacki Oct 7 '16 at 9:37
• So what ideas have you had as to how to solve this problem? – Farcher Oct 7 '16 at 11:22
• Because the collision lasts is "very short" the force acting perpendicular to the surface of the wall on the ball is very large. Thus so is the friction. Thus the inertia is transformed into vertical motion. This would mean no matter the speed the ball would move up. This doesn't seem to be a correct answer though. – TTkacki Oct 7 '16 at 15:08
• I have no idea how to even start the calculations, thus I cannot apply any formulas. If I knew which formulas to use I would have solved the task. Could you please edit this question to be acceptable this one time to show me the proper way of asking them? I am trying to learn, just nothing seems to work. – TTkacki Oct 10 '16 at 19:19