Hi! I have a question for example 5, aren't you supposed to find first the maximum height when the ball was being thrown upward? The cliff was 24m above the ground and you throw the ball upward so it means the distance should be greater than 24m? Adding the distance of the ball from the cliff and the distance from the ground to the cliff will become the maximum height for the ball.
One can define the - direction to be whatever direction they wish. It's an arbitrarily assigned convention. You just must be consistent within the problem. For instance, if the initial velocity is up and you make it + (+ is designated as up), then g must be made - since it is down. If the initial velocity is down and you make it + (+ is designated as down), then g must be + because it is down.
May you help me with this example? A stone is thrown vertically upward with a velocity of 20 m/s. a)Find the velocity after 1sec and after 2 secs b)How far up does it travel after 1 sec and after 2 secs c)How long will it take to get back to the point from which it was originally thrown?
The big idea in this algebra is you have to perform the same math operation to each side of the = sign in an effort to get the unknown variable by itself. For instance in Ex 1 ... Multiply both sides by 2 (gets rid of 1/2 on the right side. Divide both sides by -9.8 (gets rid of the -9.8 on the right side. Then square root each side (the right side now becomes t). You must do the same operations on the left side in the same order.
There are a few examples here. In general your safest method is to define down as the negative direction. Then any vector that is down has a negative sign in your calculations. It is not the only way to do it but it's the way that makes the most sense to the most students.
Thanks for the video and I have a question. In examples 1-4, there are 2 significant figures for g (9.8). Why did you use 3 significant figures in your final answer?
d would be the symbol for displacement. Displacement is a vector and has a direction. To communicate to the calculator the direction of displacement, I use - for down and + for up (and sometimes vice versa). What is important is that you keep track of up and down and are consistent within a problem as to down being negative (or the opposite).
Thank you for the video! I am a bit confused though- why is gravity negative in the first two problems? Shouldn't it be positive for downward motion then negative for upwards motion such as in example three? Positive and negative signs have been giving me a lot of issues in solving free fall problems :(
In all 5 problems the same convention is used: up is + and down is -. You can actually use the opposite convention if you like as long as you are consistent. You must use your convention (mine being up is + and down is -) to translate direction info into +/- signs. So since accel'n is always down, a = negative 9.8 m/s/s. If a ball falls down (that is, finishes below its starting point), then d is negative for down. In Ex. 3, the ball starts moving up, so the v-original is a + value for up. +/- signs can be confusing; you just have to think of it as a direction. Start with a convention like up is + and down is - and start translating direction to signs. Hope that helps. Mr. H
Upwards and downwards are directions. When we have to enter a direction into our calculator we simply decide which direction is positive and which direction is negative. There is no rule for this. It's totally the decision of the problem solver.
The math would yield an answer of -27 m/s for final velocity. This means the velocity is 27 m/s, down. The question asks for speed. Speed is a scalar with no direction so the answer is 27 m/s.
