Classical Mechanics - Kinematics

A stone is thrown at an angle 45^o above the horizontal x-axis in the +x-direction. If air resistance is ignored, which of the velocity versus time graphs shown above best represent v_x versus t and v_y versus t, respectively?

	vx versus t	vy versus t
A.	I	IV
B.	II	I
C.	II	III
D.	II	V
E.	IV	V

(GR0177 #24)

Solution:

An object such as a cannonball is fired at an angle to the ground:

• The shape of the path or its trajectory is parabolic
• In the x-direction, the object travels at constant speed
• In y-direction, we treat the object as if it were tossed directly upward (positive velocity) and then returned to the ground (negative velocity → the object reverses the direction of its motion).

Answer: C