Penguin and slide. Check my answers? I want to be prepared for the test

In summary, a sled weighing 60 N is pulled horizontally across snow by an applied force of 13 N, allowing a penguin weighing 70 N to ride on the sled without sliding off. If the penguin releases its grip on the sled, the maximum horizontal force that can be exerted on the sled before the penguin starts to slide off is 49 N. This is determined by setting the maximum static friction force of 49 N equal to the product of the penguin's mass and acceleration, and solving for the acceleration. To find the force needed to achieve this acceleration, the mass of both the sled and the penguin must be used in the equation F=ma.
  • #1
zell_D
57
0

Homework Statement


A sled weighing 60 N is pulled horizontally across snow so that the coefficient of kinetic friction between sled and snow is .100. A penguin of 70 N rides on the sled
a) The penguin digs claws into sled, what value of F do you need for the sled and penguin to move at constant speed
b) The penguin releases grip on the sled, coefficient of static friction between penguin and sled is .700, find the maximum horizontal force F that can be exerted on the sled before the penguin starts sliding off

Homework Equations


F=ma
Newton's 2nd and 3rd? law

The Attempt at a Solution


a) constant speed implied a=0
F=ma -> F=0
FN=Fg, FN=mg
Fapplied=friction
Fapplied=(.100)FN=.100*(60+70)=13N to move at constant speed

b) actually only 3 forces acting on the penguin FN Fg static friction
static friction = .700*mg
=.700(70)=49 N = max static friction threshold. So a force that's > 49 N needs to be exerted on the slide before the penguin falls off?

I am assuming kinetic friction has no role in this problem and that since acceleration is not asked for I don't have to set 49 to ma to find the max acceleration before it slides off and everything.
 
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  • #2
zell_D said:

The Attempt at a Solution


a) constant speed implied a=0
F=ma -> F=0
FN=Fg, FN=mg
Fapplied=friction
Fapplied=(.100)FN=.100*(60+70)=13N to move at constant speed
Good.

b) actually only 3 forces acting on the penguin FN Fg static friction
static friction = .700*mg
=.700(70)=49 N = max static friction threshold. So a force that's > 49 N needs to be exerted on the slide before the penguin falls off?
You found the maximum static friction force that the sled can exert on the penguin. But what you need to find is the maximum force F you can exert on the sled before the penguin starts to slide off.

I am assuming kinetic friction has no role in this problem and that since acceleration is not asked for I don't have to set 49 to ma to find the max acceleration before it slides off and everything.
That's exactly what you have to do! :wink: (Just because they don't ask for the acceleration, doesn't mean you don't need to solve for it as a step towards the solution.)
 
  • #3
ok but when i set 49 to ma, i am kind of confused as to which mass to use to find the acceleration. the sled's mass or the total mass?
 
  • #4
You are doing F = ma for the penguin only, so use the mass of the penguin.
The maximum force that can be exerted on the penguin by the sleigh is that friction force, thus the limit on the acceleration.
 
  • #5
so it would be 49=(70/9.8)a and then a = 6.86 m/s^2?
so that is the MAX acceleration this system can have before the penguin slides off right?

so in order to find the force that I need to apply on the sled to achieve this acceleration, I then use F=ma again? but this time, with the mass of the sled AND the penguin? not so sure but i am thinking about it like this:

the penguin will stay on the slide as long as the max acceleration is 6.86, so I am applying force on both masses. right?
 
  • #6
Yes on all points!
 
  • #7
hmm I think I am starting to get forces, got to get into energy next argh >.<

but thanks for the help delphi51 and doc al
 

Related to Penguin and slide. Check my answers? I want to be prepared for the test

1. What is the relationship between penguins and slides?

Penguins do not have any natural connection to slides. However, they may occasionally encounter slides in captivity or in human-made environments, such as zoos or amusement parks.

2. Can penguins slide on their bellies without a slide?

Yes, penguins are known for their ability to slide on their bellies on ice and snow. This behavior is called tobogganing and is used for transportation and play.

3. Do all penguins slide?

No, not all penguins slide. Some penguin species live in warmer climates where there is no ice or snow to slide on. They may still engage in other forms of play, but not sliding.

4. Is sliding important for penguins' survival?

No, sliding is not crucial for penguins' survival. It is a fun and sometimes helpful behavior, but penguins can thrive without it.

5. Do penguins get dizzy from sliding?

Penguins have adapted to sliding and do not get dizzy from it. They have a special organ in their inner ear that helps them maintain balance and orientation while sliding.

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