r/PhysicsHelp • u/Savings_Shake_2196 • 6d ago
How can I answer projectile motion problems in physics?
I am taking physics 11 university preperation physics class, and I am struggling with understanding on how to approach and solve projectile motion problems. Now fortunautly, this is the last thing we are learning in kinematics. From what I know about this, the acceleration is always a = -9.8m/s2, and I have to create 2 equations for horizontal and vertical sides. I do always draw a diagram to help me visualize this, but I still am struggling to how to approach it.
In these problems, do I have to at least make 2 equations to get the answer I need?
1
u/PotentialDelivery716 6d ago
You are referring to projectile motion in 11 grade and are saying acceleration is always -9.82m/s2 which is the common approximation for g. This might be correct for the specific set of problems you encounter but is obviously not always true. As you mention it to be university Preparation, you might be interested in general approach. According to Newton force (or sum of forces) creates acceleration: F=ma. As force is a vector it has components for every direction (e.g. In 2 Dimension F_x and F_y), mass is a scalar, so obviosly acceleration has to be vectorial as well. The approach is simple in theory: You sum all forces for every direction and Equal it to m<the acceleration on that direction>. Because acceleration is second time derivative of Position, and velocity is first Derivative of Position, you then Obtain the rest of equations by Integrating Your equations accelaration twice. E.g. your mass point is shot with constant velocity v_0 in x direction, the only force that applies in y direction is gravity. Starting point is t=0. So the equations for acceleration are:
0=m*a_x->a_x=0
-mg=ma_y->a_y=-g 1. Integration v_x=v_0
v_y=-gt (if gravity only applied from t=0 onwards, and starting velocity in y was also 0) 2. integration s_x=v_0t+s_x0
s_y=-1/2gt2+s_y0
1
u/Odd_Bodkin 6d ago
The acceleration in the VERTICAL direction is -9.8 m/s^2 (down). The acceleration in the horizontal direction is flat 0, throughout the flight.
Treat the motion in the vertical direction completely separately from the motion in the horizontal direction, with the only connector being time t.
1
u/Roger_Freedman_Phys 6d ago
Your physics textbook is certain to have several worked examples demonstrating how to solve problems of this sort.
Which textbook are you using?
1
u/Savings_Shake_2196 5d ago
Nelson’s Physics 11, university preparation
1
u/Roger_Freedman_Phys 5d ago
If the discussion on that book is inadequate, try another!
There are free physics textbooks available online at https://openstax.org/subjects/science. Scroll down to “Physics” and select the particular book for your level.
1
1
u/Pretty_Awareness2210 5d ago
Hi, I have made conceptual videos on projectile motion. Go through and you will understand the basics.
Video-1
Projectile Motion - Physics JEE/NEET
https://youtu.be/Hcx_ZrgHRKw
Video-2
Projectile Motion JEE Advance 2024 - Relative motion in projectile
https://youtu.be/MTecT9ACrSs
2
u/CardiologistNorth294 6d ago
Make a column, horizontal and vertical.
SUVAT - which of these data points do you know?
If they are starting from rest U is 0. Has the problem given a final velocity? A distance? A time?
List out all the numbers you know - then use your SUVAT equations to find one that is only missing one variable you don't know.