Find the acceleration of the object

[TyErd]

please open the word document.
This questions really frustrating me

 

[rl.bhat]

You can find the acceleration of the object by using
vf^2 = vi^2 + 2*a*s. vi and s is given. Find a.
This acceleration has two components. One the component of g which acts in the downward direction. And the other due to braking force, which acts in the opposite direction of the motion. In the diagram sinθ is given. (10/100).
Write down the expression for the acceleration and solve the problem..

 

[TyErd]

um to find acceleration can't you use a=gsinθ, but if you use that its 10xsin(5.740) which equaks 1.001 because if sinθ=10/100 then θ=5.74. However if I use your equation i get a=4.5m/s/s

 

[rl.bhat]

um to find acceleration can't you use a=gsinθ, but if you use that its 10xsin(5.740) which equaks 1.001 because if sinθ=10/100 then θ=5.74. However if I use your equation i get a=4.5m/s/s

The acceleration a is correct.
Now a = af - g*sinθ, where af is the acceleration due to frictional force.

 

[TyErd]

how do i calculate af?

 

[rl.bhat]

how do i calculate af?

In the problem they have asked
What is the constant braking force?
So you have find af, then the braking force = m*af.
You have found a and g*sinθ. Using the above equation find af.

 

[TyErd]

so is af = 4.500 - 1.001?, then the braking force is 1000*3.499=3499?

 

[TyErd]

so then what is the driving force?

 

[TyErd]

is it just 1000N?

 

[rl.bhat]

so is af = 4.500 - 1.001?, then the braking force is 1000*3.499=3499?

This step is wrong.
af = a + g*sinθ.
Αnd what do you mean by driving force?
Sledge moves down due to gravitational force. The frictional force stops it.

 

[TyErd]

whats the difference between a and gsinθ?

 

[rl.bhat]

whats the difference between a and gsinθ?

mg*sinθ ...> Force acting on the sledge due to gravity in the downward direction
μ*mg*cosθ...>Frictional force in the upward direction = m*af
Net retarding force acting on the sledge is
mg*sinθ - m*af = - m*a.

 

[TyErd]

ok we calculated before that gsinθ = 1.001. so that's the acceleration downwards direction. then we calculated a to be 4.500 using that equation. why are they different when there both acceleration?

 

[rl.bhat]

When you are using the equation vf^2 = vi^2 + 2*a*s. to find a, you are getting the acceleration -4.5 ms^-2. whereas g*sinθ +1. There directions are different.