Homework Help: physics

Posted by blair on Thursday, October 8, 2009 at 7:03pm.

A student throws a set of keys vertically upward to her sorority sister, who is in a window 4.30 m above. The keys are caught 1.30 s later by the sister's outstretched hand.
(a) With what initial velocity were the keys thrown?
_____________ m/s upward

(b) What was the velocity of the keys just before they were caught?
___________ m/s upward or downward

Can someone help me set up ?Or explain it please. Thank you!

physics - drwls, Thursday, October 8, 2009 at 7:23pm
(a) 4.30 = Vo*t - (g/2) t^2
= Vo*1.3 - (1/2)*9.81*(1.3)^2
Solve for Vo.
1.3*Vo = 4.30 + 8.29 = 12.59 m
Vo = 9.68 m/s

(b) Use conservation of energy
Initial KE - Final KE = M g * 4.30 m
(Vo^2 - Vf^2)/2 = g * 4.30 m

Solve for the final velocity Vf. The keys could be on the way up or down.

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