- #1
warrior2014
- 34
- 0
Newton's second law and tension!
A helicopter is lifting two crates simultaneously. One crate with a mass of 139 kg is attached to the helicopter by cable A. The second crate with a mass of 88 kg is hanging below the first crate and attached to the first crate by cable B. As the helicopter accelerates upward at a rate of 1.2 m/s2, what is the tension in each of the two cables (in kN)?
Fnet=ma
I drew a free body diagram and for the first crate (139 kg) I had tension pointing upwards and gravity pointing downwards. So I did the following calculations:
-mg + Ta= ma
Ta= m (a + g)
= 139 (1.2 +9.8)
= 1529 N
= 1.529 kN
For the second crate (88 kg), I had tension of the second crate pointing upwards, tension of the first crate pointing downwards and gravity pointing downwards. So I did the following calculations:
-mg- 1529 + Tb= ma
Tb= ma + mg + 1529
= m (a+g) + 1529
= 88 (1.2 + 9.8) + 1529
= 2497 N
= 2.497 kN
Both answers were wrong so I'm not so sure what I'm supposed to be doing for this question. Any help will be appreciated!
Homework Statement
A helicopter is lifting two crates simultaneously. One crate with a mass of 139 kg is attached to the helicopter by cable A. The second crate with a mass of 88 kg is hanging below the first crate and attached to the first crate by cable B. As the helicopter accelerates upward at a rate of 1.2 m/s2, what is the tension in each of the two cables (in kN)?
Homework Equations
Fnet=ma
The Attempt at a Solution
I drew a free body diagram and for the first crate (139 kg) I had tension pointing upwards and gravity pointing downwards. So I did the following calculations:
-mg + Ta= ma
Ta= m (a + g)
= 139 (1.2 +9.8)
= 1529 N
= 1.529 kN
For the second crate (88 kg), I had tension of the second crate pointing upwards, tension of the first crate pointing downwards and gravity pointing downwards. So I did the following calculations:
-mg- 1529 + Tb= ma
Tb= ma + mg + 1529
= m (a+g) + 1529
= 88 (1.2 + 9.8) + 1529
= 2497 N
= 2.497 kN
Both answers were wrong so I'm not so sure what I'm supposed to be doing for this question. Any help will be appreciated!