# Oxford PAT 2010, Question 25

## 9 thoughts on “Oxford PAT 2010, Question 25”

1. Mustafa says:

Hello,
Why did you take the initial upward velocity as 100*3^1/2?

1. The projectile is fired at an angle of π/3 upwards and the horizontal velocity is 100m/s, so the vertical velocity is 100tan(π/3), which is 100√3.

2. Belen says:

Hello, I don’t understand why the velocity of the car doesn’t change, since the projectile had a certain speed and becomes stationary, this would mean that if the initial momentum P was 10200 (projectile) + 200100 (car)=202000 and that doesn’t change for sure, the final velocity of the car should be 202000/210. Even if we consider that the initial velocity of the projectile in x was 200*cos alfa, it still had some velocity, which it transfers to the railcar.

3. Jemi says:

Hi, I thought that energy was scalar so you can’t split the kinetic energy into components. Could you explain why you did so above?

Thanks

1. Yes energy is a scalar, but velocity is a vector and you can split kinetic energy up into the two kinetic energies resulting from the two orthogonal components of the velocity. You can see that this is always works — it’s an instance of Pythagoras’s theorem.

4. Why have you calculated the kinetic energy in respect of the vertical velocity when you worked out the max altitude through the kinetic energy? I don’t understand that point

5. Clary says:

About the velocity of the car does not change when projectile lands, could I relate with with relative speed?

1. HI Clary. Do you mean that you could consider the relative horizontal velocity of the projectile and the car, and point out that it is zero, and therefore the velocity of the car won’t change? If so, then yes I think that would be a good answer.