Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.

Get a Professional Answer

Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.

100% Satisfaction Guarantee

Rate the answer you receive.

Ask David Your Own Question

David, Tutor

Category: Homework

Satisfied Customers: 2310

Experience: PhD in Theoretical Physics

394177

Type Your Homework Question Here...

David is online now

The lob in tennis is an effective tactic when your opponent

Customer Question

The lob in tennis is an effective tactic when your opponent is near a net. Suppose you lob the ball with an initial speed of 15 m/s an an angle of 50 degrees above the horizontal. At that instant your opponent is 10 m away from the ball. He begins to move away at 0.3 s later, hoping to reach the ball and hit it back at the moment that it is 2.1 m above its launch point. With what minimum average speed must he move? (ignore the fact that he can stretch, so the tacket can reach the ball before he does)

first calculate the time it takes the ball to reach 2.1 point above the ground we have h=vo*t*sin(50)-0.5gt^2 hence 2.1 = 11.49t - 4.9t^2 solution of this quadratic equation is t1=0.20 (this time corresponds the moment then the ball is moving up) t2=2.15 (this time corresponds the moment then the ball is moving down) only the second solution is relevant as the delay of the player is 0.3 which is more than 0.2 during 2.15 sec the ball covered the horizontal distance of d=vo*cos(50)*2.15 = 20.73 meters, so the player needs to run back 20.73-10=10.73 meters and the time he has for that is 2.15-0.3=1.85 seconds so the average speed needs to be V=d/t = 10.73/1.85 =5.8 m/s

David :

Answer: 5.8 m/s

David :

hope this helps

Customer:

Thanks..I was not sure you were online so I posted a second question as open q. Can you please take that on too.. It is something likea n airplane is flying with a velocity of 240 m/s at an angle of 30 degrees with the horizontal (in a downward dive). When the altitude of the plane is 2.4 KM a flare is released from the plane. The flare hits the target on the ground. What is the angle th... Please see on the site

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.

JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.

Web sites like justanswer.com/legal ...leave nothing to chance.

Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.

Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.

I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C.Freshfield, Liverpool, UK

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. RobinElkton, Maryland

He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here.DianeDallas, TX

Meet The Experts:

LogicPro

Engineer

Satisfied Customers:

4925

Expert in Java C++ C C# VB Javascript Design SQL HTML