What is the Maximum Safe Upward Acceleration of a Block Lifted by a Crane?

[raamishstuden]

Homework Statement

A crane has a maximum safe working load of 1.2 * 10^4 N and is used to lift a concrete block of mass 1000kg. What is the maximum safe upward acceleration of the block while being lifted?

Homework Equations

F=ma

The Attempt at a Solution

F=mα
1.2*10^4=1000*α
α= 12m/s2The answer is 2.2 m/s2

 

[PeterO]

Homework Statement

A crane has a maximum safe working load of 1.2 * 10^4 N and is used to lift a concrete block of mass 1000kg. What is the maximum safe upward acceleration of the block while being lifted?

Homework Equations

F=ma

The Attempt at a Solution

F=mα
1.2*10^4=1000*α
α= 12m/s2


The answer is 2.2 m/s2

You seem to have forgotten that while the crane is pulling up, gravity is pulling down, so the net force is much less than 1.2*10^4 N
Acceleration is the result of the net force.

 

[raamishstuden]

Oh! I got it. Here is the solution. Is it right?

F-f=ma
(1.2*10^4)-(9.81*1000)=1000*a
2190=1000a
a=2.19
=2.2 ms-2

 

[PeterO]

Oh! I got it. Here is the solution. Is it right?

F-f=ma
(1.2*10^4)-(9.81*1000)=1000*a
2190=1000a
a=2.19
=2.2 ms-2

That's more like it.