Welcome back to Physics 215. Today’s agenda: Velocity and acceleration in two-dimensional motion Motion under gravity -- projectile motion Acceleration on curved path. Current homework assignment. HW2: Ch.2 (Knight textbook): 48, 78, 82 Ch.3 (Knight textbook): 28, 32, 42
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Velocity and acceleration in two-dimensional motion
Motion under gravity -- projectile motion
Acceleration on curved path
Reminder about course website:
s – vector position
Displacement s = sF - sI, also a vector!
ax = 0
vx = v0x
x= x0 + v0xt
ay = -g
vy = v0y - gt
y= y0 + v0yt - (1/2)gt2
v0y = v0sin(q)
v0x = v0cos(q)
A ball is ejected vertically upward from a cart at rest. The ball goes up, reaches its highest point and returns to the cart.
In a second experiment, the cart is moving at constant velocity and the ball is ejected in the same way, where will the ball land?
A battleship simultaneously fires two shells at enemy ships. If the shells follow the parabolic trajectories shown, which ship will be hit first?
B. Both at the same time
D. need more information
R : when is y=0 ?
t[vy1-(1/2)gt] = 0
i.e., T = (2v)sinq/g
Is the acceleration of the object equal to zero?
v = Ds/Dt lies along
dotted line. As Dt 0
direction of v is tangent
Recall that vF+ (-vI) = Dv
For which of the following motions of a car does the change in velocity vector have the greatest magnitude? (All motions occur at the same constant speed.)
A. A 90° right turn at constant speed
B. A U-turn at constant speed
C. A 270° turn on a highway on-ramp
D. The change in velocity is zero for all three motions.
A car moves along the path shown. Velocity vectors at two different points are sketched. Which of the arrows below most closely represents the direction of the average acceleration?
A child is riding a bicycle on a level street. The velocity and acceleration vectors of the child at a given time are shown.
Which of the following velocity vectors may represent the velocity at a later time?
A biker is riding at constant speed clockwise on the oval track shown below.
Which vector correctly describes the acceleration at the point indicated?
Biker moving around oval at track shown below.constant speed
As point D is moved closer to C, angle approaches 90°.
Acceleration vectors for ball swung in a horizontal circle at constant speed v
What is the magnitude of the acceleration?a = v2/R