Two projectiles, X and Y, are fired into the air from the same place on level ground and reach the same maximum height, as shown.
Projectile X is fired vertically upwards and projectile Y is fired at an angle to the horizontal.
Air resistance is negligible.
Which statement is correct?
A X and Y are at rest at their maximum heights.
B X and Y are fired with the same speed.
C X and Y take the same time to return to the ground.
D X and Y travel the same distance.
ANSWER: C
The Physics behind the answer:
- A projectile motion can be split into 2 motions - one along the vertical and the other along the horizontal. Assuming that air resistance is negligible, the projectile
- experiences a force [gravity] along the vertical and so it will accelerate at rate 9.81 m s-2.
- experiences no force along the horizontal i.e. zero acceleration and travels at constant horizontal velocity.
- You can say therefore that the motion of Y is the same as the motion of X along the vertical plus a constant velocity motion along the horizontal.
- This means that when sent up at the same time with the velocity of X the same as the vertical component of velocity of Y [which should be as seen in the graph], they will return to the ground at the same time as they have the same acceleration [9.81 m s-2].
- The only difference is that Y has moved horizontally due to its horizontal velocity/motion.
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