An attacker at the base of a castlewall 3.90 m highthrows a rock straight up wit

Question

An attacker at the base of a castlewall 3.90 m highthrows a rock straight up with speed 7.40 m/s at aheight of 1.50 m above theground.
(a) Will the rock reach the top of thewall?
(b) If the rock will reach the top, what is its speed? If it willnot, what initial speed must it have to reach thetop?
(c) Find the change in speed of a rock thrown straight down fromthe top of the wall at an initial speedof 7.40 m/s andmoving between the same two points.
(d) Does the change in speed of the downward-moving rock agree withthe magnitude of the speed change of the rock moving upward betweenthe same elevations? Explain physically why it does or does notagree.


(a) Will the rock reach the top of thewall?
(b) If the rock will reach the top, what is its speed? If it willnot, what initial speed must it have to reach thetop?
(c) Find the change in speed of a rock thrown straight down fromthe top of the wall at an initial speedof 7.40 m/s andmoving between the same two points.
(d) Does the change in speed of the downward-moving rock agree withthe magnitude of the speed change of the rock moving upward betweenthe same elevations? Explain physically why it does or does notagree.


(a) Will the rock reach the top of thewall?
(b) If the rock will reach the top, what is its speed? If it willnot, what initial speed must it have to reach thetop?
(c) Find the change in speed of a rock thrown straight down fromthe top of the wall at an initial speedof 7.40 m/s andmoving between the same two points.
(d) Does the change in speed of the downward-moving rock agree withthe magnitude of the speed change of the rock moving upward betweenthe same elevations? Explain physically why it does or does notagree.

Explanation / Answer

(a) Will the rock reach the top of thewall?
maximum height reached=1.5+7.4*7.4/19.6=4.2938m
hence the rock reach the top of the wall
(b) If the rock will reach the top, what is its speed? If it willnot, what initial speed must it have to reach thetop?
u=7.4m/sec v=?
a=-9.8m/sec*sec
h= 4.2938-3.6=0.6938m
v=7.4*7.4-2*9.8*0.6938=6.4163m/sec

(c) Find the change in speed of a rock thrown straight down fromthe top of the wall at an initial speedof 7.40 m/s andmoving between the same two points.
change in speed is same .
(d) Does the change in speed of the downward-moving rock agree withthe magnitude of the speed change of the rock moving upward betweenthe same elevations? Explain physically why it does or does notagree.
yes.the change in speed of thedownward-moving rock agree with the magnitude of the speed changeof the rock moving upward between the same elevations.
it agree when there is no air resistance .
and it does not agree when there is airresistance.

(a) Will the rock reach the top of thewall?
maximum height reached=1.5+7.4*7.4/19.6=4.2938m
hence the rock reach the top of the wall
(b) If the rock will reach the top, what is its speed? If it willnot, what initial speed must it have to reach thetop?
u=7.4m/sec v=?
a=-9.8m/sec*sec
h= 4.2938-3.6=0.6938m
v=7.4*7.4-2*9.8*0.6938=6.4163m/sec

(c) Find the change in speed of a rock thrown straight down fromthe top of the wall at an initial speedof 7.40 m/s andmoving between the same two points.
change in speed is same .
(d) Does the change in speed of the downward-moving rock agree withthe magnitude of the speed change of the rock moving upward betweenthe same elevations? Explain physically why it does or does notagree.
yes.the change in speed of thedownward-moving rock agree with the magnitude of the speed changeof the rock moving upward between the same elevations.
it agree when there is no air resistance .
and it does not agree when there is airresistance.

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