Force and motion -- A water drop on the windscreen of a car

[shk]

Homework Statement

I am helping someone with her homework and need help with part C.

Relevant Equations

I have attached all my working.
F=ma

Hi
Please help me with part C.
I have answered the question and have attached it for you to see.

 

[haruspex]

Yes, the wind will exert a horizontal force, and R may also change.
You will need to make some assumption about the nature of F to decide whether that will change,
You also know that the drop stays on the windscreen, which gives you information relating the acceleration of the car to the acceleration of the drop.

 

[shk]

Yes, the wind will exert a horizontal force, and R may also change.
You will need to make some assumption about the nature of F to decide whether that will change,
You also know that the drop stays on the windscreen, which gives you information relating the acceleration of the car to the acceleration of the drop.

F is friction. When car accelerates, the drop goes to the left with the same acceleration so R has to increase since it needs a bigger component to the left . F is always directly proportionality to R so F increases as well.

Yes, the wind will exert a horizontal force, and R may also change.
You will need to make some assumption about the nature of F to decide whether that will change,
You also know that the drop stays on the windscreen, which gives you information relating the acceleration of the car to the acceleration of the drop.

Thanks for the comment. F is friction. When car accelerates, the drop goes to the left with the same acceleration so R has to increase since it needs a bigger component to the left . F is always directly proportionality to R so F increases as well. Is this correct ?

 

[haruspex]

F is friction... F is always directly proportionality to R so F increases as well.

Water is not solid. When it flows over a surface, it does not all need to move at once.
I would think a raindrop can stay where it is on a sloping surface because of surface tension. That does not increase when the normal force increases.
Anyway, it is not true that static frictional force is proportional to normal force. It is only ever as large as it needs to be to prevent sliding. $\mu_sN$ is only the upper limit of the magnitude of the frictional force.