Period of spring-mass system and a pendulum inside a lift

[songoku]

Homework Statement

Two systems, mass - spring system and simple pendulum is put inside a lift. When the lift is at rest , the period of the mass - spring system is $T_s$ and period of simple pendulum is $T_p$. When the lift moves upward with constant acceleration, then
(a) Both periods stay the same
(b) Both periods increase
(c) Both periods decrease
(d) $T_p$ stays the same but $T_s$ decreases
(e) $T_p$ changes but $T_s$ stays the same

Relevant Equations

$T= 2\pi \sqrt{\frac{L}{g}}$

$T=2\pi \sqrt{\frac{m}{k}}$

Based on the formulas, variable $m , k, L,g$ do not change so my answer is (a) but it is not correct.

Why?

Thanks

 

[jbriggs444]

$T= 2\pi \sqrt{\frac{L}{g}}$

$T=2\pi \sqrt{\frac{m}{k}}$

Based on the formulas, variable $m , k, L,g$ do not change so my answer is (a) but it is not correct.

What happens to your apparent weight when the lift you are in is accelerating upward?

 

[songoku]

What happens to your apparent weight when the lift you are in is accelerating upward?

My apparent weight will increase

 

[jbriggs444]

My apparent weight will increase

What does that mean for apparent g?

 

[songoku]

What does that mean for apparent g?

I am not sure

$$N - W=ma$$
$$N=m(a+g)$$

Is apparent g = a + g? So the apparent g will increase?

If yes, is it the same for the pendulum? The apparent g will increase so the period will decrease, becoming:
$$T=2\pi \sqrt{\frac{L}{a+g}}$$

Thanks

 

[jbriggs444]

I am not sure

$$N - W=ma$$
$$N=m(a+g)$$

Is apparent g = a + g? So the apparent g will increase?

If yes, is it the same for the pendulum? The apparent g will increase so the period will decrease, becoming:
$$T=2\pi \sqrt{\frac{L}{a+g}}$$

Yes.

If you are in a lift accelerating upward and do not look out the window, the situation is indistinguishable from an increase in gravity. As you have correctly calculated, the result is a decrease in the pendulum's period.

 

[songoku]

Thank you very much jbriggs444