# Thread: looks easy but stuck on one step

1. ## looks easy but stuck on one step

Not going to write out the whole question but here's the basics:

h = -0.5t^2g + d

h = height
t = time
g = gravity
d = starting height (which is 100m)

Find how long it takes a rock to fall to a height of 25m on each planet.
gravity for mars is g = 3.7m/s^2, gravity for venus is g = 8.9m/s^2

so I've got 25 = -0.5t^2(3.7) + 100

and that's as far as I can get lol, all the previous questions have been in the form of y = ax^2 + bx + c, and I'm find with those, I'm just not sure what to do when there's multiplication. Can I multiply a number by a squared number? Do I do something to the squared number first? Maybe just multiply it by -0.5t to get t (bx)?

2. Originally Posted by vicereine
Not going to write out the whole question but here's the basics:

h = -0.5t^2g + d

h = height
t = time
g = gravity
d = starting height (which is 100m)

Find how long it takes a rock to fall to a height of 25m on each planet.
gravity for mars is g = 3.7m/s^2, gravity for venus is g = 8.9m/s^2

so I've got 25 = -0.5t^2(3.7) + 100

and that's as far as I can get lol, all the previous questions have been in the form of y = ax^2 + bx + c, and I'm find with those, I'm just not sure what to do when there's multiplication. Can I multiply a number by a squared number? Do I do something to the squared number first? Maybe just multiply it by -0.5t to get t (bx)?
25 = -0.5t^2(3.7) + 100

=> -75 = -0.5t^2(3.7)

=> 150 = t^2(3.7)

=> 150/(3.7) = t^2

Now square root both sides.