Question

How to find average speed with a given initial speed, theta, and delta x?
I know average speed= total distance/total time, but I am given an initial speed, an angle and delta x.

Mark throws a ball to Daniel with an initial speed of 20 m/s at an angle of 45 degrees. If they are initially 55 m apart, calculate the average speed Daniel has to run to catch the ball.


the answer is: 4.9 m/s

but how would I go about solving this?? Help, I'm stuck.

Answer 1

Use the vertical component to find time in air.

Hf=hi+Viy*t-1/2 g t^2
0=0=20sin45*t-4.9t^2

t(20sin45-4.9t)=0
t= 20sin45/4.9 and that is time in air.

avg velocity= horizontal distance/time
= 55m/t