Newtons 2nd law another problem

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To solve the problem of a block on a frictionless inclined plane, the relationship between kinetic energy (KE) and potential energy (PE) is crucial. Initially, the block has all kinetic energy, which can be calculated using KE = 1/2mv^2, where v is the initial velocity. As the block ascends, it converts this kinetic energy into potential energy, described by PE = mgh, until it comes to a stop at its maximum height. The total energy remains constant throughout the motion, allowing for the determination of the distance traveled up the incline and the time taken to reach that position. Utilizing these energy equations will lead to the solution for both parts of the problem.
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A block is propelled up a 48 degree frictionless inclined plane with an initial velocity of 1.20 m/s...A) how far up the plane does the block go before coming to a rest. B) How long does it take to move to that position?


for part A) , i have initial velocity and I am looking for x (distance)

i'm stuck...not sure what to do
 
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If you learned about kinetic and potential energy then the problem is not to bad. You just have to use the relationship: KE + PE = Etotal (where Etotal should always be constant). So intially when you "launch" the block, your energy is all KE and zero PE. But when it reaches its maximum height then your energy is all PE. See what you can do...

Hint: KE = 1/2mv^2 and PE = mgh
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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