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# Projectile Motion Question (M2) Help plz

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1. Hi, I don't seem to be getting the right answer for this question. Essentially, you have a dart that's shot at a board 3 metres away from it at 21ms-1. The point of projection is in line with the bullseye. I've calculated that the dart lands 0.1 metres below the bullseye. But, my calculation for the angle that the dart makes with the horizontal the moment it hits the board seems to be wrong. I do tan-1(0.1/3) to get the angle, which is 1.909... But that answer is wrong, the right answer is 3.81 degrees below horizontal. I'd appreciate any help.
2. (Original post by student1856)
Hi, I don't seem to be getting the right answer for this question. Essentially, you have a dart that's shot at a board 3 metres away from it at 21ms-1. The point of projection is in line with the bullseye. I've calculated that the dart lands 0.1 metres below the bullseye. But, my calculation for the angle that the dart makes with the horizontal the moment it hits the board seems to be wrong. I do tan-1(0.1/3) to get the angle, which is 1.909... But that answer is wrong, the right answer is 3.81 degrees below horizontal. I'd appreciate any help.
You need to find the final velocity, v, of the vertical component of motion.
s = -0.1 (as you said it fell 0.1m below the bullseye)
u = 0 (as the initial velocity was 21m/s horizontally)
a = -9.8 (due to gravity)

Solve for v using v²=u²+2as to get v = 1.4m/s

Then create a triangle using the two velocities, 21 and 1.4.

tan^-1(1.4/21) = 3.81°
3. (Original post by miless090)
You need to find the final velocity, v, of the vertical component of motion.
s = -0.1 (as you said it fell 0.1m below the bullseye)
u = 0 (as the initial velocity was 21m/s horizontally)
a = -9.8 (due to gravity)

Solve for v using v²=u²+2as to get v = 1.4m/s

Then create a triangle using the two velocities, 21 and 1.4.

tan^-1(1.4/21) = 3.81°
Hi, yes I was using the vertical and horizontal distances to try and calculate the angle the the dart makes with the horizontal. I should have been using the vertical and horizontal velocities instead. I found the vertical velocity to be 1.4ms-1 when you do V=u+a*t(0+9.8x1/7). Then I used the tan rule to calculate the angle that the dart makes with the horizontal(tan-1(1.4/21)). This ended up giving me the correct answer of 3.81 degrees below horizontal. Simple Really. Thanks very much.

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