2 Problems

[SilverFalcon]

Hi, this is my first post on here hope I can answer some in the future. I've finished everything except these two problems. I've got the answers except I can't figure out how to arrive at the conclusions.

1) A 4.2-kN piano is to be slid up a 3.5-m frictionless plank at a constant speed. The plank makes an angle of 30° with the horizontal. Calculate the work done by the sliding the piano up the plank. A: 74.103 J

I know I have to use this f=f(parallel)/angle and w=f*d but other than that I'm not too sure.

2) A car is driven at a constant speed of 76 km/h down a road. The car's engine delivers 48 kW of power. Calculate the average force that is resisting the motion of the car. A: 23000 N

This one seems too easy for me to be asking am I missing something really obvious?

Thanks for looking and hopfully you can help me, btw my test is tommorow, heh. :yuck:

[dextercioby]

Hi, this is my first post on here hope I can answer some in the future. I've finished everything except these two problems. I've got the answers except I can't figure out how to arrive at the conclusions.

1) A 4.2-kN piano is to be slid up a 3.5-m frictionless plank at a constant speed. The plank makes an angle of 30° with the horizontal. Calculate the work done by the sliding the piano up the plank. A: 74.103 J

I know I have to use this f=f(parallel)/angle and w=f*d but other than that I'm not too sure.

Make the drawing and then use the geometry to find the tangential component of the force...

2) A car is driven at a constant speed of 76 km/h down a road. The car's engine delivers 48 kW of power. Calculate the average force that is resisting the motion of the car. A: 23000 N

This one seems too easy for me to be asking am I missing something really obvious?

What is the relation between force,velocity & mechanical power...??BTW i think your answer is off a size order...

Daniel.

Thanks for looking and hopfully you can help me, btw my test is tommorow, heh. :yuck:[/QUOTE]