# Projectiles

• Jan 8th 2010, 02:01 AM
NathanBUK
Projectiles
Hi, I have my mechaincs 1 exam on Friday next week and projectiles are one of my weaker topics so I was wondering if anyone can confirm my answers that I got.

A ball is kicked from the point P on a horizaontal surface. it leaves the surface with a velocity of 20ms-1 at an angle of 50degrerss above the horizontal and hits the surface for the first time at the point Q. Assume that the ball is particle that moves only under the influence of gravity.

(b)Find the distance between the points P and Q. (previous question asked to show the time was 3.13s)

I got 40.2m

(c) If a heavier ball were projected from P with the same velocity, how would the distance between P and Q, calculated using the same modelling assumptions, compare with your answer to part (b)? Give reason for your answer.

I said it was only influenced by gravity.

(d) Find the maximum height of the ball above the horizontal surface.

I got 12.0m

(e) State the magnitude and the direction of the velocity of the ball as it hits the surface.

I said for the magnitude 20cos50 which was 12.9ms-1 and I said fo the direction 50degrees below the horizontal.

All my answers are to (3sf).

• Jan 8th 2010, 02:35 AM
Hello NathanBUK
Quote:

Originally Posted by NathanBUK
Hi, I have my mechaincs 1 exam on Friday next week and projectiles are one of my weaker topics so I was wondering if anyone can confirm my answers that I got.

A ball is kicked from the point P on a horizaontal surface. it leaves the surface with a velocity of 20ms-1 at an angle of 50degrerss above the horizontal and hits the surface for the first time at the point Q. Assume that the ball is particle that moves only under the influence of gravity.

(b)Find the distance between the points P and Q. (previous question asked to show the time was 3.13s)

I got 40.2m

(c) If a heavier ball were projected from P with the same velocity, how would the distance between P and Q, calculated using the same modelling assumptions, compare with your answer to part (b)? Give reason for your answer.

I said it was only influenced by gravity.

(d) Find the maximum height of the ball above the horizontal surface.

I got 12.0m

(e) State the magnitude and the direction of the velocity of the ball as it hits the surface.

I said for the magnitude 20cos50 which was 12.9ms-1 and I said fo the direction 50degrees below the horizontal.

All my answers are to (3sf).

Well done, you've got this more-or-less correct. Just one or two fairly minor points:

For part (c), I think you should say:
The distance between P and Q would be unchanged, because we are assuming that the particle is influenced only by gravity.
(which I suspect is what you meant, but didn't actually say so).

For (e) the magnitude of the velocity at Q is $20 \text{ m s}^{-1}$ at an angle of $50^o$ below the horizontal. You have just given the magnitude of its horizontal component.

• Jan 8th 2010, 02:46 AM
NathanBUK
Quote:

Hello NathanBUKWell done, you've got this more-or-less correct. Just one or two fairly minor points:

For (e) the magnitude of the velocity at Q is $20 \text{ m s}^{-1}$ at an angle of $50^o$ below the horizontal. You have just given the magnitude of its horizontal component.