Consider a rock that is thrown off a bridge of height 71 m at an angle ? = 25° w

Question

Consider a rock that is thrown off a bridge of height 71 m at an angle ? = 25° with respect to the horizontal?
Consider a rock that is thrown off a bridge of height 71 m at an angle ? = 25° with respect to the horizontal as shown in the figure above. If the initial speed the rock is thrown is 11 m/s, find the following quantities:
(a) The time it takes the rock to reach its maximum height.
s

(b) The maximum height reached by the rock.
m

(c) The time at which the rock lands.
s

(d) The place where the rock lands.
m

(e) The velocity of the rock (magnitude and direction) just before it lands.
Magnitude Direction
m/s °

Explanation / Answer

solution: (a) time taken to reach maximum height = usin?/g                                                            = 11*sin 250/9.8                                                            = 11*0.422/9.8                                                            = 0.42 sec (b) maximum height= H = u2 sin2 ?/2g                                  = (11) 2 (0.422)2 /2*9.8                                  = 121*0.17/19.6                                  = 20.57/19.6                                  = 1.04 m (c) time of flight = T= 2usin?/g                                 = 2*11*0.422/9.8                               = 0.94 sec (d) Range = R = u2/g sin 2?                    = 121/9.8*0.766                    = 16.13 m (e) v = v u2+g2t2         = v(121+88.35)         = 14.46 m/s towards earth towards earth

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