What magnitude of force must the worker apply to move the crate

In summary, the factory worker must apply a force of 30.4 kg to move the crate at a constant velocity. This work is done when the crate is pushed a distance of 4.00 m.
  • #1
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hi I'm new here i wanted your help in solving these two questions i tried several times to solve them but the computer kept showing that the amswer is wrong ((on mastering physics site)) so please i need the answers to those problems and fast because the chapter will be closed in an hour.

1.A factory worker pushes a 30.4kg crate a distance of 4.00 m along a level floor at constant velocity by pushing downward at an angle of 28.0 below the horizontal. The coefficient of kinetic friction between the crate and floor is 0.255 .

A.What magnitude of force must the worker apply to move the crate at constant velocity?
Take the free fall acceleration to be 9.8
B.How much work is done on the crate by this force when the crate is pushed a distance of 4.00 ?
Take the free fall acceleration to be 9.8

2.A pump is required to lift a mass of 790 of water per minute from a well of depth 13.8 and eject it with a speed of 18.1 .

A.How much work is done per minute in lifting the water?
Take the free fall acceleration to be = 9.80
B.How much in giving the water the kinetic energy it has when ejected?
C.What must be the power output of the pump?
Take the free fall acceleration to be = 9.80 .

NOTE; all the quantities are in SI units.
 
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  • #2
please i tried hard i solved all my 5 problems but those two i just can't get them right
 
  • #3
show your work, let's see where you went wrong.
 
  • #4
ok the first one i tried to solve using this equation:
Fcos(-28)-coe.k. (w) + Fsin(-28)=0

and the answer was wrong so ofcourse i wasn't able to find the work

the second problem was hard for me because i didn't take caculus at the first place
 
  • #5
why do you add Fsin(-28)?

hint: pushing a box downwards and foreward on a plane when you don't have friction is like pushing it forward... (with only the horizontal component).
when you got friction, and you push something downwards you add you force to its weight...
 
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  • #6
I don't understand your equation. Start with the fundamental equation

[tex]F = \mu N[/tex]

and express N as the sum of the weight of the crate plus the vertical component of the pushing force...
 
  • #7
fargoth said:
why do you add Fsin(-28)?

hint: pushing a box downwards and foreward on a plane when you don't have friction is like pushing it forward... (with only the horizontal component).
when you got friction, and you push something downwards you add you force to its weight...

i did that but it kept telling me it's wrong please help me i don't have much time it's due to 6 pm today:cry:
 
  • #8
neji006 said:
i did that but it kept telling me it's wrong please help me i don't have much time it's due to 6 pm today:cry:

You didn't do that in your earlier equation.

Friction = uN, what is N? It is the weight of the crate + the additional force supplied by the worker. The weight of the crate is mg, and the additional force is the vertical component of his push, it's obvious you understand this, but you are not equating it to N, perhaps because you didn't draw a free body diagram?

So, N = mg + Fv (Fv is the vertical part of the push, you will have to supply this), then

Friction = u(mg + Fv)

I agree with the other poster that you are making a mistake using -28 as the angle measure, just because it is below the horizontal doesn't make it a -28. It won't bother your cosine, but it will affect your sine function.

I don't see any units in the second problem, sorry to say. How much water in how much time? Cubic meters? In any case, I don't think you need calculus for this.

It's late. I'm going to bed.

Dorothy
 
  • #9
Hope you got it done neji006 ;)
 
  • #10
i did , boy i was nervous thanks guys i got 94% on the work and kinetic energy chapter.
 

1. What is the definition of force?

Force is a physical quantity that can cause an object to accelerate or change its state of motion. It is typically measured in Newtons (N).

2. How is force related to the movement of an object?

In order for an object to be moved, a force must be applied to it. The magnitude of the force will determine how much the object will accelerate or change its motion.

3. What factors affect the magnitude of force needed to move an object?

The mass of the object and the surface it is moving on are the main factors that affect the magnitude of force needed to move it. Friction and gravity may also play a role.

4. How can the magnitude of force needed to move a crate be calculated?

The magnitude of force can be calculated using Newton's Second Law: Force = mass x acceleration. The mass of the crate and the desired acceleration can be used to determine the necessary force.

5. Is there a minimum or maximum magnitude of force needed to move a crate?

The magnitude of force needed to move a crate can vary depending on the mass of the crate and the surface it is being moved on. However, there is a minimum force needed to overcome static friction and a maximum force that may cause the crate to slide or break.

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