Question

A wet bar of soap (m= 0.150 kg) slides down a ramp 2.0m long at an angle of 7.3 degrees. How long does it take to reach the bottom?

Answer 1

Since it is a wet bar of soap, I assume there is no friction.
If we draw the forces diagram, we found that there is a resultant force of the normal reaction N and the gravitational force F=mg and that F=mgsin(alpha).
That force is equal to F=ma, therefore mgsin(alpha)=ma=>a=gsin(alpha).
From the equation t=sqrt(2x/a), we get that t is approximately 1,8 seconds.
Keep in mind that this is actually independent of the mass of the body.

Answer 2

ohhhh i did F=mgcos. could you explain why it's sin? also thanks

Answer 3

no the answer is infact 1.8 ...

Answer 4

Oh yeah.. Now i forgot taking the square root LOL... 1,8 seconds is infact the right answer.
I hope that this sketch helps you :P

Answer 5

ohhh i see, i calculated a y component for gravity as well which doesn't really exist in this case. well anyway, thanks! :)