AQA A-Level physics help

Here is the question: "A ball is dropped into a cylinder filled with paint. The process is then repeated with a ball of the same diameter but twice the mass. How would the terminal velocity differ and why?". I understand that in order to reach terminal velocity, the weight (W) must equal the drag (D) + upthrust (U) and initially, the drag is much greater than the weight, so the ball decelerates. I also understand that the ball has a larger mass and so greater weight. What does this mean for the terminal velocity, however? Does it mean that, as the ball has a greater weight, the terminal velocity would be reached sooner as W = U + D. D is initially much larger than weight so must decrease and as W is a larger value, it decreases such that U+D = W quicker? However I've always been taught that mass is directly proportional to the terminal velocity. Help please.?

Reply 1

Joinedup

Could be more to it.

A ball could be equal density to the paint, in which case it would have a terminal velocity of zero... Or it could be less dense and float back to the surface.

Reply 2

Incrediblezed

Original post by Joinedup

Could be more to it.

A ball could be equal density to the paint, in which case it would have a terminal velocity of zero... Or it could be less dense and float back to the surface.

Oh yeah sorry I forgot to mention the ball comes to rest inside the paint.

Reply 3

Joinedup

Paint seems like an odd choice cos you generally can't see through it to make timings easily - I'm aware some paints branded 'non drip' have viscosity modifiers added which makes them turn to a semi solid jelly when they're not being stirred - they are non Newtonian liquids which makes them different from most household liquids.

anyway you will be interested in the difference between the density of the ball and the density of the paint

some information on this type of investigation including a probably useful equation https://qualifications.pearson.com/content/dam/pdf/A%20Level/Physics/2015/teaching-and-learning-materials/AS-and-A-level-Physics-Core-Practical-4---Viscosity-(Student,-Teacher,-Technician-Worksheets).pdf