Average Speed problem?
So I have a Physics question, and it's super simple, but for some reason the books says I am wrong. And I am, but I don't know why.
So the question is: A marble is released from one rim of a hemispherical bowl of diameter 50.0 cm and rolls down and up to the opposite rim in 10.0 s. Find the average speed.
I know the equation is Distance/Elapsed time. I keep getting 5 cm/s as my answer because I divide 50/10. But my book says the answer should be 7.85 cm/s.
Can someone please tell me what I am doing wrong? Thanks!
Comments
Yeah you are dividing the wrong number. The number they give you is the diameter. You are going to want to find the length of the semicircle.
Circumference = 2*Pi*r
you only want half the circumference soo
distance = pi * r
distance = pi * 25 cm
Take that number and divide by 10 and it should equal that.
That marble didn't roll the diameter; it rolled the semi circumference. So S = pi D/2 = Vavg T and Vavg = pi()*50/(2*10) = 7.853981634 = 7.85 cm/s ANS.