Here are a few questions. I urgently need help. Thanksssss!
1. Usually, we are told that at the maximum displacement, when v = 0 ms-1, the acceleration is only that of gravity, 9.81 ms-2. May I know if this case only applies in circumstances when air resistance is negligible? If yes, what happens if A.R must be taken into account, acc. is lower?
2.A ball is thrown with a velocity of 26 ms-2 vertically upwards and has 0ms-1 at 1.8s.
Just after the ball leaves the thrower's hands, it has a downward acceleration of approximately 20ms-1. Explain how this is possible.
My explanation is rather brief, it circles around the fact that the downward forces Wball and Fd (drag force) > g so acceleration will have value greater than 9.81 ms-2. Do I have to make calculations to show that the downward acceleration is around 20ms-2?
3.When you have acceleration-time graph in the -ve region and moving downwards (which originates from a point in the +ve region), how do you know that velocity is in +ve or -ve region? Because -ve acceleration doesn't mean -ve velocty. I always have probs trying to translate v-t and s-t graphs given a-t graphs, especially when the a-t graphs are curves... any helpful sources to help me understand better? I need a lot of representations to understand.
4. X
O___________________P________________Q
*X in the above diagram represents max height reached by ball x, which is directly above P
Ball X of mass m is projected with a speed of u from O at an angle alfa (let's give it a symbol 'a') above the horizontal and it raeches its max. height directly above point P.
Ball Y of mass 2m is projected towards P with speed of 2u from O also at an agle of 'a' above the horizontal. Deduce Y's horizontal displacement when it reaches it s max.height. (Q is twice as far away from O as P)
Not sure how throwing another ball of double the mass and spped will have implications on the horizontal displacement... I suppose this is a projectile question but I really dont see how knowing ball Y has double the mass of ball X enables me to solve this question. Do help me in solving this question.
A bit rushy, so I giving short answers. Do try to figure out :)
1) Yes. Remember Terminal Velocity in O levels?
2) Just Air Resistance acting downwards
3) Just now a-t graph comes from v-t (gradient of v). And by finding the gradient, or in maths... differentiating, you will lose some data when you work backwards unless you have some initial condition. That's why you always have a +c when you integrate
Diff v = a
Int a = v
4) Mass doesn't affect. It's the initial speed that affects. Because vertical acc g is independent of mass.
The mass there is to test your understanding and concepts.