Solving Free Falling Objects Problem

[steph35]

Homework Statement

A girl throws her set of keys to her friend upward who is in a window 3.90m above. the keys are caught later at 1.30s by the friends hand.

Homework Equations

a. With what initial velocity were the keys thrown?
b. What was the velocity of the keys just before they were caught?

The Attempt at a Solution

a. i tried finding change in x/change in t but got the wrong answer
b. i tried using a kinematic equation and solving for Vfinal but got the wrong answer...

 

[LowlyPion]

Homework Statement

A girl throws her set of keys to her friend upward who is in a window 3.90m above. the keys are caught later at 1.30s by the friends hand.

Homework Equations

a. With what initial velocity were the keys thrown?
b. What was the velocity of the keys just before they were caught?

The Attempt at a Solution

a. i tried finding change in x/change in t but got the wrong answer
b. i tried using a kinematic equation and solving for Vfinal but got the wrong answer...

Consider using the equation:

$$x = x_0 + v_0 t + (1/2) a t^2$$

 

[baba89]

It seems like you are on the right track with using kinematic equations to solve this problem. However, there are a few key pieces of information missing from the homework statement that are necessary to solve for the initial velocity and final velocity of the keys.

First, we need to know the acceleration of the keys. In this case, we can assume that the keys are in free fall, so the acceleration would be equal to the acceleration due to gravity (9.8 m/s^2).

Next, we need to know the initial height of the keys. We are given the final height (3.90m) and the time it takes for the keys to reach that height (1.30s), but we need the initial height in order to calculate the initial velocity.

Once we have the initial height and acceleration, we can use the kinematic equations to solve for the initial velocity and the final velocity. It is important to note that the final velocity will be equal to the negative of the initial velocity, since the keys are caught at the same height from which they were thrown.

In summary, to solve this problem, we need to know the acceleration, the initial height, and the final height of the keys. With this information, we can use the kinematic equations to calculate the initial velocity and the final velocity of the keys.