While standing on a bridge 19.0 m above the ground, you drop a stone from rest.
ID: 1274665 • Letter: W
Question
While standing on a bridge 19.0 m above the ground, you drop a stone from rest. When the stone has fallen 2.70 m, you throw a second stone straight down. What initial velocity must you give the second stone if they are both to reach the ground at the same instant? Take the downward direction to be the negative direction. While standing on a bridge 19.0 m above the ground, you drop a stone from rest. When the stone has fallen 2.70 m, you throw a second stone straight down. What initial velocity must you give the second stone if they are both to reach the ground at the same instant? Take the downward direction to be the negative direction.Explanation / Answer
Delay in throwing 2nd stone, t= time taken for 1st stone to cover 2.70m
2.70=ut+0.5gt2
2.70*0t+0.5*9.8t2
t=0.742 sec
Total time taken for stone to fall 19.0m.
19.0=0t+0.5*9.8t2
t=1.969 sec
Distance travelled by stone1=distance travelled by stone2
u1t +0.5gt2=u2(t-0.742)+0.5g(t-0.742)2
0*1.969 +0.5*9.8*1.9692=u2*(1.969-0.742)+0.5*9.8*(1.969-0.742)2
u2=9.47 m/s
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