Homework Help: Physics

Posted by shmza on Wednesday, October 26, 2011 at 4:01pm.

A place kicker must kick a football from a point 37.1 m from a goal. As a result of the kick, the ball must clear the crossbar, which is 3.05 m high. When kicked the ball leaves the ground with a speed of 19.8 m/s at an angle of 53° to the horizontal.
(a) By how much does the ball clear or fall short of clearing the crossbar?
(b) Does the ball approach the crossbar while still rising or while falling?

Physics - Henry, Thursday, October 27, 2011 at 9:33pm
Vo = 19.8m/s@53Deg.
Xo = hor = 19.8cos53 = 11.92m/s.
Yo = ver = 19.8sin53 = 15.81m/s.

a. t = (Yf - Yo) / g,
t(up) = (0 - 15.81) / -9.8 = 1.613s.

d=Vo*t + 4.9*t^2 = 12.753 - 3.05=9.703m
0 + 4.9t^2 = 9.703,
t^2 = 1.98,
t(dn) = 1.41s. to fall to 3.05m.

Dh = Xo(t(up)+t(dn)),
Dh = 11.92(1.41+1.613) = 36m=hor dist.

Falls short by: 37.1 - 36 = 1.1m.

b. While falling.
Physics - Anonymous, Tuesday, October 2, 2012 at 9:41pm
a. Falls short by 3 m
Physics - Anonymous, Tuesday, October 2, 2012 at 9:51pm
a. Falls short by 3 m

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