Lok said:Could you give the complete solution or solving pathway chosen?
Well in which direction are you solving for time? And how would that translate in your equation?PhysicallyAbel said:They solved for time first, as I did, using the equation for position. X=VoT+1/2AT^2.
Their equation is: -20=0t+1/2(-9.8)t^2. When they solved for t they got t=2 seconds.
This is where I am confused because the equation states initial velocity is 7.0m/s, yet they use 0. That's where I need help.
Lok said:Well in which direction are you solving for time? And how would that translate in your equation?
Supposing the X axis is horizontal, your gravity is not present in the X axis, only the initial velocity, so solving for time there would give no ideea of when the projectile hits the ground. But it would in the Y, you have gravity, and the initial velocity in a vertical Y direction would be?PhysicallyAbel said:We are using the positive x-axis for the direction of time. They got +2 seconds, I'm getting +2.8 seconds. Does that clear it up? I'm kind of confused so I apologize if I'm not making sense.
dean barry said:Image dropping another projectile from rest at the same time, they would both strike the ground a the same time.
Ignore the horizontal component of motion for now ( a constant 7 m/s)
Regardless of the horizontal velocity, the time taken to fall the 20 m to ground is the same.
The projectile accelerates (vertically) from 0 m/s
g is +ve as it acts in the direction of motion, so
u = 0 m/s
g = 9.8 (m/s)/s
s = 20 m
Use one of Newtons rules to calculate the time t to fall the 20 m from rest
The point is your initial velocity is in the horizontal direction and gravity is vertical. Your equation applies only in a one dimensional setup so on a line, if you have conditions pointing in another direction than your equations dimension would permit you have to do a transformation with angles and sin and cos (usually at this point in your physics study). In your problem you have basically 2 dimensions. X horizontal and Y vertical. The equation in Y has only gravity and a 0 initial velocity, and in the X, zero gravity and your initial velocity of 7m/s. It's the same equation used in two different directions there the velocity and force vectors point at an angle of 90 deg.PhysicallyAbel said:This is what I'm not understanding. If the initial velocity is actually 0 m/s, then why would the equation state it is 7.0 m/s.
Lok said:The point is your initial velocity is in the horizontal direction and gravity is vertical. Your equation applies only in a one dimensional setup so on a line, if you have conditions pointing in another direction than your equations dimension would permit you have to do a transformation with angles and sin and cos (usually at this point in your physics study). In your problem you have basically 2 dimensions. X horizontal and Y vertical. The equation in Y has only gravity and a 0 initial velocity, and in the X, zero gravity and your initial velocity of 7m/s. It's the same equation used in two different directions there the velocity and force vectors point at an angle of 90 deg.
Lok said:It would be close to the need of such notions. And if not studied do ask your teacher about these and your problem.
But just to clarify the problem somehow visually (with the coolest most powerfull GPU of imagination)
When viewed from the far left (or right). The projectile will look like standing still at start and accelerating towards the ground with g until it hits it.
When viewed from the far top, your projectile will be looking like it is moving at a constant speed from start, until for some reason it comes to a complete stop.
The two motions are completely independent until the ground is hit, just as they should appear in the math.
One-dimensional motion refers to the movement of an object in a straight line, with no change in direction. This can be represented on a graph as a straight line, with the distance or position of the object changing over time.
The main difference between one-dimensional and two-dimensional motion is the number of dimensions in which the object is moving. One-dimensional motion occurs along a single straight line, while two-dimensional motion involves movement in two perpendicular directions (such as up/down and left/right).
Displacement is the change in an object's position or location from its starting point to its ending point. It is a vector quantity, meaning it has both magnitude (the distance of the movement) and direction (the orientation of the movement).
Velocity is defined as the rate of change of an object's displacement over time. In one-dimensional motion, it can be calculated by dividing the change in position (displacement) by the change in time. Velocity is also a vector quantity and includes both magnitude (speed) and direction.
Acceleration is the rate of change of an object's velocity over time. In one-dimensional motion, it can be calculated by dividing the change in velocity by the change in time. It is also a vector quantity and includes both magnitude (speed of change) and direction (whether the object is speeding up, slowing down, or changing direction).