# Calculating the final speed using Force/Time Graph

1. Oct 6, 2011

### Nizzeh

1. The problem statement, all variables and given/known data

A golfer strikes a stationary golf ball, and the force applied by the club on the ball varies as shown in the graph below. Use this graph to determine the final speed of the golf ball. The mass of the golf ball is 0.1kg

2. Relevant equations

Area of triangle = 1/2bh (then times by two for the full area.) Or AvgFt=m(v-u)

3. The attempt at a solution

I tried avgF*t= m(v-u) and put 100*0.04=0.1(v-0) = 4/0.1 = 40m/s

also tried Area of Triangle = 1/2bh = 0.5*0.04*100 = 2 Then 2*2 = 4m/s to get the full triangle.

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2. Oct 6, 2011

### Windowmaker

Final speed? As in t= 80?

3. Oct 6, 2011

### SammyS

Staff Emeritus
Welcome to PH Forums.

The average Force during the 80 milliseconds of contact is 50 Newtons.

What does the Impulse - Momentum Theorem say? -- or -- How is impulse related to momentum?

4. Oct 6, 2011

### Nizzeh

it says Time of Contact / ms so I assume it's milliseconds.

5. Oct 6, 2011

### Nizzeh

Impulse = Momentum?

6. Oct 6, 2011

### SammyS

Staff Emeritus
Not quite right. Look again.

7. Oct 6, 2011

### Nizzeh

Impulse = Change in Momentum.

8. Oct 6, 2011

### SammyS

Staff Emeritus
Yes, that's it. Although, in this case, the ball starts out having zero momentum.

9. Oct 6, 2011

### Nizzeh

Ok so how did you get this? Im confused? Sorry about this.. what calculation would I do?

10. Oct 6, 2011

### SammyS

Staff Emeritus
The impulse is the area under the graph, that's the area of the triangle. You have that right as 4 N-s = 4 kg-m/s .

You answer of 40 m/s also looks to be correct.

11. Oct 6, 2011

### Nizzeh

So which is the actual answer? you wrote 50 above which kinda confused me.

12. Oct 6, 2011

### SammyS

Staff Emeritus
What did I say about 50 Newtons ? I said it was the average force during the 80 ms of contact. That's all

13. Oct 6, 2011

### Nizzeh

Ok so the formula I'd use and the solution is what?