Solve Motion Problem: 50 m Drop Time & Velocity

[mikep]

can someone help me with this problem? A hot air balloon is descending at a rate of 2.0 m/s when a passenger drops a camera. (a) If the camera is 50 m above the ground when it is dropped, how long does it take to reach the ground? (b) What is its velocity just before it lands? Let upward be the positive direction for this problem.

i did part a by this formula. 50 = (-2.0m/s)t + (1/2)(-10m/s2)t2
s2 = s squared t2 = t squared
i tried to solve for t and i got 2.9, but that not the right answer. anyone know what i did wrong?

 

[Doc Al]

sign convention problem

It's a sign convention problem. Compared to where it starts to fall, the final position is -50 m, not +50 m.

 

[mikep]

ok so if i change the sign to -50 i get t = 2.96 that's what i had before. its not right

 

[Doc Al]

ok so if i change the sign to -50 i get t = 2.96 that's what i had before. its not right

What makes you think that your answer is incorrect? (Note that you'll get a slighty more accurate answer using g = 9.8 m/s^2.)