Find Velocity: Homework Equations & Solutions

[rqureshi24]

Homework Statement

screenshot of problem: imgday.net/?di=8RMN

Homework Equations

PE = MGH
KE = 1/2 x m x v^2
V = d/t

The Attempt at a Solution

I know how to find the PE & KE, but I stumped at finding the velocity and it keeps saying I get the wrong answer or would it just be 20 m/s?

 

[collinsmark]

Homework Statement

screenshot of problem: imgday.net/?di=8RMN

Homework Equations

PE = MGH
KE = 1/2 x m x v^2

The above formulas are very important to solving this problem.

V = d/t

Be careful with that one. v = d/t only applies for constant velocity (i.e. if a = 0). But acceleration is involved with this problem. The projectile is certainly not moving at a constant velocity.

The Attempt at a Solution

I know how to find the PE & KE, but I stumped at finding the velocity and it keeps saying I get the wrong answer or would it just be 20 m/s?

The answer may just be 20 m/s, but you should be able to explain why that is.

If you've already found KE, then use your KE = ½mv² formula. Solve for v.

 

[rqureshi24]

Be careful with that one. v = d/t only applies for constant velocity (i.e. if a = 0). But acceleration is involved with this problem. The projectile is certainly not moving at a constant velocity.

Oh, thank you so much for the tidbit. My physics teacher never explained to us like that. It's true that you learn something new everyday. :)

The answer may just be 20 m/s, but you should be able to explain why that is.

It's not 20 m/s, it's 20.976 and rounded to 20.98, isn't it because speed & velocity are teh same thing?

If you've already found KE, then use your KE = ½mv² formula. Solve for v.

I wish I thought of that earlier, now I got the correct answer using that formula! I feel so dumb for wasting so much time trying to figure it out.