Question

An attacker at the base of a castle wall 3.70 m high throws a rock straight up with speed 7.50 m/s at a height of 1.51 m above the ground.

(a) Will the rock reach the top of the wall?

(b) If so, what is the rock's speed at the top? If not, what initial speed must the rock have to reach the top?

(c) Find the change in the speed of a rock thrown straight down from the top of the wall at an initial speed of 7.50 m/sand moving between the same two points.

Answer 1

The distance to travell for the rock to reache the top of the wall is, 3.70m - 1.51m -2.19 m With speed u -7.50 m/s, the maximum height reached by the rock is, 750m/s 2g 2x9.8 m/s H 0.382 nm As the maximum height is less than the distance to travell to reach the top of the wall, the rock can not reach the top of the wall The required initial speed to travell the distance of 2.19 m is, u-y2gs-J2(9.8m/s*)(2.19 m) u 6.55 m/s Using the equation of motiorn v- (7.50 m/s)+(2x9.8 m/sx2 19m) v 9.95 ms