# Physics 11 question!! pls help (Kinematics)?

A golf ball rolls up a hill toward a hole. Assume that the direction towards the hole is positive.

If the golf ball starts with a speed of 2.0 m/s and slows at a constant rate of 0.5 m/s^2, what is its velocity after 2.0 seconds?

I keep getting 3.0 m/s as the final velocity but that makes no sense because its slowing down.

### 5 Answers

- WhomeLv 71 year agoFavorite Answer
You need to set your origin and positive direction and then stick with it throughout the problem

You state that the positive direction is toward the hole.

It makes sense that the origin should be at the initial position of the golf ball as it starts rolling.

In this reference frame, the initial velocity is positive and the acceleration is towards the origin or in the negative direction

v = u + at

v = 2.0 + (-0.5)(2.0)

v = 1.0 m/s

I hope this helps.

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- Anonymous1 year ago
good thing u know "keep getting 3.0 m/s as the final velocity" does not make sense.

Good job!

- AshLv 71 year ago
t=0, v=2.0 m/s

t=1, v = 2.0 m/s - 0.5 m/s = 1.5 m/s

t=2, v = 1.5 m/s - 0.5 m/s = 1.0 m/s

Using equation of motion

v = u+at

v = (+2.0) + (-0.5)(2)...............Notice initial velocity is +2.0 m/s, while acceleration is -0.5 m/s² as it is in opposite direction of initial velocity

v = 2.0 - 1.0

v = 1.0 m/s

- Steve4PhysicsLv 71 year ago
a = -0.5m/s^2

Note the negative sign as the ball is decelerating.

or (better)

F=ma . The resultant force causing slowing must act in the negative direction. So F must be negative hence a must be negative.

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- oubaasLv 71 year ago
V(2) = Vo-a*t = 2.0-0.5*2 = 2.0-1.0 = 1.0 m/sec

...and gets the hole with a final speed a bit over zero and after a total time a bit less than 4 seconds

I'm really curious how you determined that the ball actually reaches the hole. I see no evidence of a distance to the hole in the question.

haha thank u