You lean out of your window in residence (which is 12 m above the ground) and hu

Question

You lean out of your window in residence (which is 12 m above the ground) and hurl a 0.12-kg ball up to your friend, whose window is 11 m above you. What is the minimum speed with which you can throw the ball so that he just catches it (2 s.f. - you need to work to 3 s.f. to round your answer to 2)?

Suppose you throw the 0.12-kg ball at this minimum speed. Your friend misses the catch. What is the ball's kinetic energy just before it hits the ground (2 s.f.)?

The two questions above were asked previously, needed for the following question

1) If you had thrown the 0.12-kg ball downwards (instead of upwards towards your friend) with the same speed, what then would have been its kinetic energy just before hitting the ground?

Explanation / Answer

height travelled by ball=S=11 m

let it is thrown by velocity x m/s

for minimum velocity,final velocity=0 m/s

a=-9.8 m/s^2

by newton equation

v^2=u^2+2aS

x^2=2*9.8*11

x=14.683 m/s

if friend misses ball,velocity at ground (i.e. after travelling 11+12=23 m down)

v^2=u^2+2aS

v=21.23 m/s

kinetic energy=0.5*mv^2=27.05 J

if it has been directly thrown downwards

its velocity at ground(now it would travel 12 m)

v^2=2*9.8*12=235.2

v=15.336 m/s

kinetic energy=14.1 J

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.