Pole Vaulting Kinematics Problem

[physicsnobrain]

Homework Statement

A pole-vaulter leaves the ground with an upward speed of 9.5 m/s.
(a) How fast is she going when she is 2.0 m above the launch point?
(b) How long is required to reach this height?
(c) Why are there two answers to (b)?

The Attempt at a Solution

Question A and B I don't have a problem with. I worked out A to be 7.1 m/s (2 sig digs) and B to be 0.2 seconds (2 sig digs).

However it is question C I am not understanding. I feel tempted to write "because I can write the answer in seconds or I can write it in minutes". But I feel this is a silly answer, therefore I need help.

 

[CAF123]

However it is question C I am not understanding. I feel tempted to write "because I can write the answer in seconds or I can write it in minutes". But I feel this is a silly answer, therefore I need help.

When the pole vaulter goes up, she must come down.

 

[physicsnobrain]

When the pole vaulter goes up, she must come down.

So there could be one answer that measures her going up and one answer that measures her going up then coming down?

 

[CAF123]

So there could be one answer that measures her going up and one answer that measures her going up then coming down?

Yes, depending on what kinematic equation you use you will either get the two solutions automatically or not.

 

[Nickie]

In regards to question C, there are two answers to (b) because the question is asking for the time required to reach a specific height, which can be calculated using two different methods. The first method is to use the initial upward velocity of 9.5 m/s and the acceleration due to gravity to calculate the time it takes to reach a height of 2.0 m. The second method is to use the distance formula, where the distance traveled is 2.0 m, the initial velocity is 9.5 m/s, and the acceleration is the acceleration due to gravity. Both methods will give you the same answer, but they use different equations and concepts. This is why there are two answers to (b). It is important to understand and be able to use both methods in physics problem solving.