Projectile Problem: Find Time of Collision

[vivekrai]

Homework Statement

http://u.spig.in/forum/105599049.jpg

A projectile is fired at t=0 with velocity v = 20√2 m/s at an angle of 45° degrees as shown. A wall inclined at the same angle and at a distance of 40 m starts moving towards the projectile at the same time (ie., t=0) with a speed of 20m/s. Find the time at which the ball collides with the the wall.

Homework Equations

General Kinematical Equations

The Attempt at a Solution

I'm getting answer as 2(√3-1) s. Strikingly this is very similar to my friend's answer i.e, 2(√2-1) s. I don't know whose one is correct. Help me.

My Solution,

Let the base of the wall has moved a distance 40-x m at the time the ball collides with the wall. Let the height at which the collision occurs is y.
Then we have,
20t = 40-x ... (1) (for wall)
y = 20t-5t² ... (2) (for ball)
and x+y=20t ... (3) (General diagram and since angle is 45 deg)

Solving for ' t ' , a quadratic I got, t = 2(√3-1) s (Other value being negative)

 

[LawrenceC]

I get your answer.

 

[vivekrai]

Thanks for verifying.