Homework Help: Physics

Posted by Sam on Thursday, October 7, 2010 at 4:37pm.

I have a golf ballthat is hit for 0.20s at an angle to the horizontal and it hits the ground some distance away. Initial speed is 30m/s and angle of projection is 35. Calculate the time between when the ball was hit and when it first touched down.

I think it should be 30m/s cos 35/9.8.

If not correct please let me know what formula to use.

Physics-Just need a formula, please and check - Sam, Thursday, October 7, 2010 at 5:05pm
Can someone please just check this problem and let me know if its wrong and the correct formula

Thank you
Physics - bobpursley, Thursday, October 7, 2010 at 5:10pm
Well, it is correct.
Physics - drwls, Thursday, October 7, 2010 at 5:11pm
Your formula is incorrect. Dividing the horizontal velocity component by g does not get you the time of flight. Note that, with your formula, the time of flight would be zero if the ball were hit straight up.

The time of flight, T, is the time it takes the ball to go up and then come back down. Those two times are equal.

T = 2 V sin35/g
Physics - bobpursley, Thursday, October 7, 2010 at 5:13pm
drwls is correct.
Physics-I'm really confused with two different answers - Sam, Thursday, October 7, 2010 at 5:16pm
So I should say

2 times (20sin35)/9.8 = 2.34

I'm really confused because one said it's correct and you said what I did is wrong-Please help
Physics - bobpursley, Thursday, October 7, 2010 at 5:17pm
reread.
Physics - drwls, Thursday, October 7, 2010 at 7:10pm
The time of flight is 2*(30sin35)/9.8 = 3.51 seconds.

I do not understand why the question began with a statement that the ball is hit for 0.2 s. You do not need that bit of information to answer the question about the time of flight. You could use it and the ball's momentum leaving the club face to calculate the average force of the club on the ball.
Physics - Sam, Thursday, October 7, 2010 at 8:04pm
Thank you, I appreciate it-I understand it now

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