Kinematics Question 414

Question: A body dropped from top of a tower fall through 40 m during the last two seconds of it’s fall. The height of tower it’s (g=10m/s2)

Options:

A) 60 m

B) 45 m

C) 80 m

D) 50 m

Show Answer

Answer:

Correct Answer: B

Solution:

Let the body fall through the height of tower in t seconds. From, Dn=u+a2(2n1) we have, total distance travelled in last 2 second of fall it’s D=Dt+D(t1)

=[0+g2(2t1)]+[0+g2[2(t1)]1]

=g2(2t1)+g2(2t3)=g2(4t4)

=102×4(t1)

or, 40=20(t1) or t=2+1=3s distance travelled at t second is s=ut+12at2=0+12×10×32=45 m



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