Homework Help: physics

Posted by bob on Thursday, August 9, 2012 at 7:24pm.

two objects are thrown from the top edge of a cliff with a speed of 10 m/s. one object is thrown straight down and the other straight up. if the first object hits the ground in 4.0 second, the second hits the ground in ________ seconds after the first object.

physics - MathMate, Thursday, August 9, 2012 at 9:06pm
Assume no air resistance.

For the object thrown downwards,
t=4 s
vi=-10 (+ve upwards)
g=-9.8 m/s²
S=vi*t+(1/2)gt²
=-10*4+(1/2)(-9.8)(4²)
=-118.4 m

For the object thrown downwards,
t=unknown
vi=+10 (+ve upwards)
g=-9.8 m/s²
S=vi*t+(1/2)gt²
-118.4=+10*t+(1/2)(-9.8)(t²) ...(1)

Solving the quadratic equation (1), we get
t=-4 or t=296/49

Can you take it from here?

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