How Is the Impulsive Force Calculated During a Mobile Phone's Impact?

[depre87]

Homework Statement

Mobile phone is dropped onto a hard floor from a height of 1.5m. The mass of the mobile phone is 0.2 kg. After the impact, the phone bounces to a maximum height of 50 mm. The phone is estimated to be in contact with the floor for 0.005s. Which is of the following is the closest to the average value of the impulsive force during the impact?

Homework Equations

F dt = dP
dP = mv1 - mv0

The Attempt at a Solution

so what i basically tried to do was calculate v1 and v0 then can find F but the answer is supposed to be 257 N where as I am getting ~177N
so i calculated the velocities using conservation of energy and found v0 to be 5.42 m/s and v1 to be 0.99 m/s and then rearrange to solve for F.

 

[ehild]

You did not take the sign of the velocities into account.

ehild

 

[depre87]

oh wow I am so silly... thankyou so much!