Basic Mechanics - Projectiles Q's having problems

[hmax]

Homework Statement

In a film stunt a car is driven over a cliff at 15ms^-1, the ground at the top of the cliff being level. The wreckage is 45m horizontally from the foot of the cliff.

What is the vertical height that the car has fallen?

Homework Equations

Im not sure but I am guessing s=ut+1/2at^2 should be used here.

The Attempt at a Solution

I've attempted to use the equation above, using v=u+at to get a value for t and using v=0, a=-9.8 and u=15. Now after finding a value for t and plugging that into the s=... eqn I am not getting the right answer.

Am i going about this the wrong way? Thanks a lot for your help.

 

[Joshrk22]

Use x = x0 + v0t + .5at^2
The car is not accelerating so all you need is x = v0t. Plug in your values...

45 = 15t
t = 3 seconds

Using x = .5gt^2
x = .5 * (9.8) * 3^2
x = 44.1 m

 

[ogb p]

Hello Q,

It seems like you are on the right track using the equations of motion. However, in this problem, we are dealing with projectile motion, which involves both horizontal and vertical components of motion. Therefore, we need to use separate equations for the horizontal and vertical components.

For the horizontal component, we can use the equation: x = ut, where x is the horizontal distance, u is the initial velocity, and t is the time. We know that the horizontal distance is 45m and the initial velocity is 15ms^-1. Therefore, we can rearrange the equation to solve for t, which gives us t = x/u = 45/15 = 3 seconds.

For the vertical component, we can use the equation: y = ut + 1/2at^2, where y is the vertical displacement, u is the initial velocity, a is the acceleration due to gravity (which is -9.8ms^-2), and t is the time. We know that the initial vertical displacement is 0, since the car starts at the top of the cliff, and we are trying to find the vertical height, which is represented by y. Therefore, we can rearrange the equation to solve for y, which gives us y = 1/2at^2 = 1/2(-9.8)(3)^2 = -44.1m.

However, we need to keep in mind that the value of y we calculated is actually the displacement from the top of the cliff to the ground. To find the actual vertical height that the car has fallen, we need to take into account the height of the cliff itself. If we assume that the cliff is 10m high, then the total vertical height that the car has fallen is 10m + (-44.1m) = -34.1m. This means that the car has fallen 34.1m below the top of the cliff.

I hope this helps clarify the problem and how to approach it. If you have any further questions, please don't hesitate to ask. Good luck with your studies!