Physics problem from ENGG1811...Please help!!! (1 Viewer)

[EmJoy]

In a typical cricket field, a boundary fence is approx 70 metres away from the centre. To hit a six, say a ball needs to be at least 4 metres off the ground when it crosses the boundary fence (in order to make it unreachable by a possible fielder).

Calculate the minimum required initial velocity (in km/hr) to hit a six for a ball hit at the angles of 10, 20, 30 and 40 from the horizontal.



I'm stuck. Please help!!!

 

[angrygeorge]

hey, hope this helps, (im still in yr 12 so i will be using 3 unit maths to try and solve it, don't know if you count air resistance in your course though).

The equations you will need are vertical displacement= -half x g x time squared + V x time x sin(30) = 4 (minimum vertical displacement). Now the other equation is horizontal displacement = V x time x cos(30) = 70 (boundary is 70m away). Rearranging this equation gives time=70/Vcos(30). Subing this time value into the vertical displacement equation, making V squared the subject then finding it are the last steps. Repeat this method for the other angles. my answer for the 30 degree angle is 59km/h (don't know if it is right it is a pretty rough draft)

 

[random-1006]

hey, hope this helps, (im still in yr 12 so i will be using 3 unit maths to try and solve it, don't know if you count air resistance in your course though).

The equations you will need are vertical displacement= -half x g x time squared + V x time x sin(30) = 4 (minimum vertical displacement). Now the other equation is horizontal displacement = V x time x cos(30) = 70 (boundary is 70m away). Rearranging this equation gives time=70/Vcos(30). Subing this time value into the vertical displacement equation, making V squared the subject then finding it are the last steps. Repeat this method for the other angles. my answer for the 30 degree angle is 59km/h (don't know if it is right it is a pretty rough draft)

lol that answer looks correct and well done but look at the time the question was posted, also incase you dont know engg1811 is a computing course, so its not actually about formulas and such, its more about programming.

nevertheless, i think you are correct, maybe you have to check your units however, it looks a bit not right with the numbers, remember you are using metres with projectile motion