In: Physics
A soccer player kicks the ball toward a goal that is 25.0 m in front of him. The ball leaves his foot at a speed of 17.0 m/s and an angle of 36.0 ° above the ground. Find the speed of the ball when the goalie catches it in front of the net.
Let us consider the upwards direction as positive and the downwards direction as negative.
Gravitational acceleration = g = -9.81 m/s2
Initial velocity of the ball = V1 = 17 m/s
Angle the ball is kick at = = 36o
Initial horizontal velocity of the ball = V1x = V1Cos = (17)Cos(36) = 13.75 m/s
Initial vertical velocity of the ball = V1y = V1Sin = (17)Sin(36) = 9.992 m/s
Distance of the ball from the goal = R = 25 m
Time taken by the ball to reach the goal = T
There is no horizontal force acting on the ball therefore the horizontal velocity of the ball remains constant.
R = V1xT
25 = (13.75)T
T = 1.818 sec
Speed of the ball when the ball reaches the goal = V2
Horizontal velocity of the ball when it reaches the goal = V2x
V2x = V1x
V2x = 13.75 m/s
Vertical velocity of the ball when it reaches the goal = V2y
V2y = V1y + gT
V2y = 9.992 + (-9.81)(1.818)
V2y = -7.843 m/s
V2 = 15.8 m/s
Speed of the ball when the goalie catches it in front of the net = 15.8 m/s