1) find the value of the planck mass. (2) A student throws aset of keys vertical
ID: 1763655 • Letter: 1
Question
1) find the value of the planck mass. (2) A student throws aset of keys vertically upward to her sorority sister, who is in awindow 4.00m above. the keys are caught 1.50s later by sister'soutstretched hand.(i) with what velocity were the keys thrown?(ii)what was the velocity of the keys just before they were caught?3) A child throws a ball to his sister who is 20.00m away,the ball reaches its maximum height 1.50s(i) with what velocity wasthe ball thrown(ii) what was the velocity of the ball just beforeit was caught?
Explanation / Answer
1) find the value of the planck mass. Sorry, not enough information (2) A student throws a set of keys verticallyupward to her sorority sister, who is in a window 4.00m above. thekeys are caught 1.50s later by sister's outstretched hand.(i) withwhat velocity were the keys thrown?(ii) what was the velocity ofthe keys just before they were caught? (i)There could be a trick. Lets check. For an object to fall 4.0mit will reach a speed V=gt ant it will take t=(2h/g). Let'scompute: t= (2x4.0/9.8)= 0.9s and the key traveled 1.5 sec. The1.5 s is a total travel time requiring the keys to travel past thesister before being caught by her outstretched hand. That ist= t1 + t2 + t3 where t2 = t3 we have t= t1 +2t2 and sincet=1.5 s and t2= (t-t1)/2 = (1.5 - 0.9)/2=0.3s. Now the total time going up is tup= 0.9 + 0.3=1.1 s and V0 = gt = 9.8 x 1.1 =10.8 m/s and (ii)Vf= gt2 Vf= 9.8 x 0.3 = 2.9m/s - 3) A child throws a ball to his sisterwho is 20.00m away, the ball reaches its maximum height 1.50s(i)with what velocity was the ball thrown(ii) what was the velocity ofthe ball just before it was caught? Since the ball reaches its max height in 1.5 s the verticalcomponent must have been Vv = gt = 9.8 x 1.5=14.7 m/s assuming that the total time in flight was 2x1.50=3.0s we have thehorizontal velocity Vh is Vh= S/t = 20/3.0= 6.7m/s Please let me know if you have any further questions.
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