Gravity Tension

Classical Mechanics Level 2

The mass of a lift is 2000 kg. When the tension in the supporting cable is 28000 N, then its acceleration is

30 m / s − 2 30 m/s^{-2} upwards 4 m / s − 2 4 m/s^{-2} upwards 30 m / s − 2 30 m/s^{-2} downwards 4 m / s − 2 4 m/s^{-2} downwards

Sravanth C. by Sravanth C. , 21, India

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1 solution

Caleb Townsend
Mar 14, 2015

T = F + W = m a + m g = m ( a + g ) a = T m − g a = 28000 2000 − 10 = 14 − 10 = 4 T = F + W = ma + mg = m(a + g) \\ a = \frac{T}{m} - g \\ a = \frac{28000}{2000} - 10 = 14 - 10 = 4

Also, when the lift is at rest, T = W . T = W. When accelerating upwards, T > W . T > W. And when accelerating downwards, T < W . T < W. In this case, 28000 > 20000 , 28000 > 20000, so it is accelerating upwards. Thus the answer is 4 m s 2 upwards \boxed{4\ \frac{\text{m}}{\text{s}^2} \text{ upwards}}

By the way, there is a typo in the answers as of this writing; the unit of acceleration is m / s 2 , m/s^2, not m / s − 2 . m/s^{-2}.

1 Helpful 0 Interesting 0 Brilliant 0 Confused

Thanks! I didn't notice it, But I can't change it.

@Calvin Lin sir, can you please edit the answers.

I was not able to do so!

Sravanth C. - 6 years, 3 months ago

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