Kinematics help..

[ctonn]

Hi everyone,

 

This is my first post on this forum which I stumbled across while searching for physics help on google. Anyway Im going to try to make this short. Im taking grade 12 physics and so far we are doing review and I remember nothing. Om going to post a few questions and hopefully you can give me specific break down on how to do it. Ill give it a shot and post my solution or if Im unable to do it, ill ask for your help. PS I would really appreciate you guys giving me a general way of approachign these questions that makes it easy for me to determine what Im looking for and the shortest way to get there.

Well here are the questions

 

1) A basketball is thrown straight up in the air, then caught on its way down. Prove that the time it takes to go up is equal to the time it takes to fall back down.

 

2) A bal at the end of a string is swung in a horizontal circle above a persons head at a speed of 2.0m/s. Is the ball undergonig uniform motion? Explain your answer.

 

3) Batman is sitting in the Batmobile at a stoplight. As the light turns green, Robin passes Batman in his lime-green Pinto at a constant speed of 60km/h. If Batman gives chase, accerlerating at a constant rate of 10km/h/s, determine

a) how long it takes batman to attain the same speed as Robin.

b) How far batman travels in this time.

c)how long it takes for Batman to catchup to robin

 

29) A child is running at her maximum speed of 4.0m/s to catch an icecream truck, which is stopped at the side of the road. When the child is 20m from the truck, the icecream truck starts to accelerate away at a rate of 1.0m/s^2. Does the child catch the truck. solve algebraically.

( This one kinda confuses me. Does it mean distance is equal when she catches up??)

 

Look forward to your excellent strategies.

-ctonn

[Mercurial]

for the first one you have to prove that t(up) = t(down)

the best equation for this is v = vo + at where a is gravitational acceleration

 

rearrange the equation to:

 

(v-v0)/g = t

 

and go from there. you have to figure out the velocity at the peak of its trajectory to finish it off (I won't give you the entire answer, but this should hlep a bit).

 

#2 I think uniform motion implies a constant speed (direction is not important) so you have to prove or disprove that.

#3

The first part is real easy: how long does it take Batman going at 10km/h/s to reach 60 km/h

The second part is using the time you found in part 'a' to determine the distance (d) in 'b'

the third part

 

d = v0t + 0.5at^2

 

Batman is at a stop implying initial velocity of 0 and Robin has a constant speed implying no acceleration.

 

What are you going to set equal to each other?

 

Solve for t

 

29) The child starts 20m behind the truck (draw a diagram) so you're right the distances have to be equal if she ever catches up. The other way to think about this is at a constant velocity how long does it take her to get to the point where the truck was and what is the speed of the truck at that point and if there's any possible way she could catch up at that point.

 

Hope this helps

[ctonn]

for the first one you have to prove that t(up) = t(down)

the best equation for this is v = vo + at where a is gravitational acceleration

 

rearrange the equation to:

 

(v-v0)/g = t

 

and go from there. you have to figure out the velocity at the peak of its trajectory to finish it off (I won't give you the entire answer' date=' but this should hlep a bit).

 

#2 [b']I think uniform motion implies a constant speed (direction is not important) so you have to prove or disprove that.[/b]

#3

The first part is real easy: how long does it take Batman going at 10km/h/s to reach 60 km/h

The second part is using the time you found in part 'a' to determine the distance (d) in 'b'

the third part

 

d = v0t + 0.5at^2

 

Batman is at a stop implying initial velocity of 0 and Robin has a constant speed implying no acceleration.

 

What are you going to set equal to each other?

 

Solve for t

 

29) The child starts 20m behind the truck (draw a diagram) so you're right the distances have to be equal if she ever catches up. The other way to think about this is at a constant velocity how long does it take her to get to the point where the truck was and what is the speed of the truck at that point and if there's any possible way she could catch up at that point.

 

Hope this helps

 

Thanks it helped alot, but could you clarify the bold part. and for #29 is it enough to get the formulas for distance for the child and the truck and set it equal to each other and then find time?

 

Also can you tell me your answers so I can compare? Also Ive got a couple more questions.

 

A falling flowerpot takes 020s to fallpast a window that is 1.9m tall. From what height above the top of the window was the flower pot dropped.

so t=.20

a=9.8m/s^2 [down]

and the formula is d=v1 + 1/2at^2

Is this right?

 

32) A person standing on the roof of a building throws a rubber ball down with the velocity of 8.0m/s. Does the ball slow down while falling?

 

34) A stone is dropped off a cliff of height. At the same time a second stone is thrown straight upward from the base of the cliff iwht an initial velocity. Assuming that the second rock is thrown hard enough at what time will the two stones meet?

[s pepperchin]

you should consult your physics book on those two bold parts and see what it says. The info given is enough to figure it out with being given the answer.