Projectiles launched horizontally quiz
pro a is launched horontally at a speed of 20.meters per second from the top of a cliff and strikes a level surface below,3.0 seconds later. projectile b is launched horizontally from the same location at a speed of 30.meter per second. what is the time it takes projectile b to reach the ground?

3.0 seconds

Explanation:

The time of flight of a projectile (the time it takes to reach the ground) does not depend on the horizontal motion, but only on its vertical motion.

In fact, the time of flight is determined by the suvat equation:

where

s is the vertical displacement

u is the initial vertical velocity (0, in case of these two projectiles)

g = 9.8 m/s^2 is the acceleration of gravity (assuming downward as positive direction)

t is the time of flight

Re-arranging the equation, we get

We see that this time depends only on s (the heigth of the cliff) and g: therefore, since the two projectiles are launched from the same height, they take the same time to reach the ground, 3.0 seconds.

grav potential energy

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.