Package A Races Down the Ramp: How Long Does it Take?

[mags]

Two packages at UPS start sliding down the 20 degree ramp.Package A has a mass of 5.0kg and a coefficient of friction of 0.20. Package B has a mass of 10 kg and a coefficient of 0.15. how long does it take package A to reach the bottom?

http://img362.imageshack.us/my.php?image=knightfigure0825pe6.jpg

 

[Quincy]

The question isn't very clear; does package B push on package A and help it accelerate?

 

[mags]

that's all I'm given...

 

[mathmate]

tan(20) =0.36 > 0.2, so the sliding that just started will continue.
So resolve the mass into a normal and a downward (along the slide) component.
Subtract the frictional force will give you the downward force.
Dividing the force by the mass gives the acceleration.
Use the usual formulae for acceleration as a function of distance and speed to find the time required to travel the down ramp of length L.