Question that i am finding really hard

[n_ds]

Hi

I tried this question a couple times, couldn't figure it out, thought maybe you guys could help.

1. The maximum load that can safely be supported by a rope in an overhead hoist is 400N. What is the maximum acceleration that can safely be given to a 25kg object being hoisted vertically upward?

I hope someone can help.

Thanks

 

[Doc Al]

What's the net force on the object if the rope is pulling as hard as it can?

Hint: Identify all forces acting on the object.

 

[n_ds]

i can't figure out net force as i do not have acceleration...all i have is what is the max load the rope can take which is 400, the gravity which is -9.8 as it is going upwards and the 25 kg load

 

[Doc Al]

First find the net force, then use it to find the acceleration.

What forces act on the object? Hint: There are two forces acting. What is the magnitude and direction of each force?

 

[n_ds]

I am not sure how to find the net force. Am i right in asuming that the 2 forces acting on the object, is the downward force of m*g and the upwards force of m*-g?

 

[Doc Al]

Am i right in asuming that the 2 forces acting on the object, is the downward force of m*g and the upwards force of m*-g?

Gravity acts downward on the object with a force equal to mg. And, no, the upward force does not equal -mg, otherwise the net force would be zero... no acceleration at all.

Besides gravity, what force acts on the object? Hint: Isn't the rope attached to the object?

 

[n_ds]

is it 400 N?

so Fnet = 400 - mg?

 

[Doc Al]

That's it!

 

[n_ds]

ok so then this is what i think the solution would be

Fnet = 400 - mg

a= Fnet / m
a= (400 - (25)(9.8))/25

and that should give me the answer i need. That does that seem right to u?

 

[Doc Al]

Perfecto...

 

[n_ds]

thanks so much for the help i really appreciate it