What is the force exerted on a 380 kg piano on a ramp with an incline of 27*?

[lemonlee]

Homework Statement

a 380 kg piano slides 3.9m down a ramp with an incline of 27* and is kept from accelerating by a man pushing parallel to the incline. Find the force exerted by the man, the work done by the man on the piano, the work done by the force of gravity, and the net work on the piano. Ignore friction.

Homework Equations

F=ma
W=F*d*cos27

The Attempt at a Solution

Once i get the force exerted by the man, I know what to do, I just can't get the right answer. I drew out a force diagram and then tried the equation, but can't get to the given answer of 1700N

 

[asleight]

Homework Statement

a 380 kg piano slides 3.9m down a ramp with an incline of 27* and is kept from accelerating by a man pushing parallel to the incline. Find the force exerted by the man, the work done by the man on the piano, the work done by the force of gravity, and the net work on the piano. Ignore friction.

Homework Equations

F=ma
W=F*d*cos27

The Attempt at a Solution

Once i get the force exerted by the man, I know what to do, I just can't get the right answer. I drew out a force diagram and then tried the equation, but can't get to the given answer of 1700N

I think you've assigned the wrong trig. function to the angle. Using \sin(3\pi/20), you get 1692N, which, after keeping 2 sig. figg., results in 1700N...

 

[lemonlee]

so I can assume that the net force is zero because the piano is accelerating, right? wouldn't that just make the force exerted by the man 4.45N?

I think i might be missing a step

 

[asleight]

so I can assume that the net force is zero because the piano is accelerating, right? wouldn't that just make the force exerted by the man 4.45N?

I think i might be missing a step

...RIght, well, because the piano isn't accelerating, the sum of the forces is zero. So, the force exerted by the man was imposed after motion began and is equal and opposite that of the x-component of gravity acting upon the piano.

 

[lemonlee]

oh i see what i forgot, I didn't multiply by the mass, I was just solving for F=a...

oops!
thank you for explaining that :)

 

[asleight]

oh i see what i forgot, I didn't multiply by the mass, I was just solving for F=a...

oops!
thank you for explaining that :)

You're very welcome.