Calculate the work done by the sliding the piano

[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.

 

[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. [/QUOTE]

 

[wais]

Hi there, great job on finishing everything except for these two problems! Let's work through them together.

1) To calculate the work done by sliding the piano, we need to use the formula W = Fd, where W is the work, F is the force, and d is the distance. In this case, we have the force (4.2 kN) and the distance (3.5 m), but we need to find the actual force that is acting on the piano.

Since the plank is frictionless, the only force acting on the piano is its weight, which is equal to its mass (m) times the acceleration due to gravity (g). We can find the mass of the piano by dividing its weight (4.2 kN) by the acceleration due to gravity (9.8 m/s^2). This gives us a mass of approximately 428.6 kg.

Now, we can find the force that is acting on the piano by using the formula F = mg, where m is the mass we just calculated and g is the acceleration due to gravity. This gives us a force of approximately 4.2 kN.

Next, we need to find the component of this force that is parallel to the plank. To do this, we use the formula F(parallel) = F * cosθ, where θ is the angle between the force and the plank. In this case, θ is 30°, so we have F(parallel) = 4.2 kN * cos30° = 3.64 kN.

Finally, we can calculate the work done by sliding the piano by using the formula W = F(parallel) * d, where d is the distance the piano is being slid up the plank. In this case, d is 3.5 m. So, W = 3.64 kN * 3.5 m = 12.74 kJ. However, the question asks for the answer in joules, so we need to convert kJ to J by multiplying by 1000. This gives us a final answer of W = 12.74 kJ * 1000 = 12,740 J.

2) This problem is a bit easier since we are given the power (P) and the speed (v) of the car. We can use the formula P = Fv, where P is the power, F is the force, and