Question

You and your roommate plot to drop water balloons on students entering your dorm. Your window is 30m above the sidewalk. You plan to place an X on the sidewalk to mark the spot a student must be when you drop the balloon. You note that most students approach the dorm at about 3m/s .

How far from the impact point do you place the X?

Answer 1

Answer 2

In this answer figures have been changed, but this may help you.

Height of room abovesidewalk   =   65ft   =   65 *0.3048   m

   h   =   19.81   m

   By second equation ofmotion

   h   =   u* t + (1/2) * g * t²

   u   =   0   asthe balloon are dropped. Hence

   19.81   =    *t + 0.5 * 9.8 * t²

   t   =   ?4.04   =   2.01   s

   In this time the student onsidewalk must walk the distance 'd' between Xmark and impact point.

   d   =   v *t   =    1.7 *2.01   =   3.42   m

   So the mark would be made at 3.42 m fromimpact point

Answer 3

s=ut+1/2at²

for falling ballon

s=30m and u=0

so time required for it to come down

30=0+1/2 x9.8 t²

t=2.47S

since they are moving with velocity 3m/s

position x=vt=3x2.47=7.42m away from window