What is the Velocity if there is no Kinetic Energy but there is a Potential Energy?

Question

There is an inclined plane. The height is 20m. There are 4 stages for the ball in it. The first is when it was on top, which is 20m. The second is when it was at the 12m part of it. The third when it was on the 6m part. And the last was 0. The given Initial Velocity was 0 and the mass is 5kg. In the table, Potential Energy for A-C wasn't given, but D was 0. In the Kinetic Energy, A has 0 and the rest is for us to find out. And lastly, in the Velocity, A had 0 and the rest was for us to find out.

For Potential Energy I've already found A-C. Since there was no Velocity, I couldn't find the Kinetic Energy because there was no Velocity, but to find Velocity, I need the square root of Kinetic Energy multiplied by to all over Mass.

So how can I find the Velocity or Kinetic Energy. Or just help me find the Velocity.

Answer 1

Assuming no friction.

A.........PE = mgh = 980 NM , KE =0

B.........PE =12*980/20 = 588 NM, KE = 392 NM

C..........PE = 6*980/20 = 294 NM , KE = 686 NM

D..........PE = 0, KE = 980 NM



at any point PE +KE = PE at A

Answer 2

I don't understand the inclined plane, sounds more like steps. A picture would help.

Here is the way to think about this. Neglecting friction: everywhere the ball is on the ramp:

it's PE + KE at that height will sum to the PE at 20m (KE at 20m =0).

The initial PE = mgh=5*9.8*20=980J

At 12m, the height has decreased by 8m which means the PE is less: 5*9.8*12=588J

which means the KE at that point must be the difference:

980-588 = 392J = 1/2 * 5 *V^2 => V = sqrt(2*392/5) =12.5 m/s

At h=6m PE =5*9.8*6=294J 980-294 = 686 = 1/2 * 5 * V^2 => V V = sqrt(2*686/5) ==16.6m/s

So the further down, the faster the ball rolls which makes sense of course. As the PE decreases, the KE increases the same amount which is only true without friction.

At h=0 the PE is 0 and the KE must be 980J

980 = 1/2 * 5 *V^2 => V = V = sqrt(2*980/5) =19.8m/s

Answer 3

In you example, the initial velocity is ZERO.



So the ball is NOT moving.



Hence, Velocity = 0.0 >==============< ANSWER



NO K.E. = 0.0 >===================< ANSWER