Physics homework questions

[azn ho]

Pelicans tuck in their wings to fall freely when diving for fish. A fish near the surface of the water needs 0.10s to take evasive action. A pelican 25.0m above the water starts its dive. The fish first notices the pelican when the pelican is 5.0m above the water.
Does the pelican go hungry, or does it catch its prey?

An object starts from rest and travels in a straight line for 5s with a uniform acceleration of 4ms^-2. It continues to move with the uniform velocity acquired for a further 12s and it is finally brought to rest with a deceleration of 2.5 ms^-2.
Calculate the distance travelled and the time taken.

Thanks!

[methodsboy]

Pelicans tuck in their wings to fall freely when diving for fish. A fish near the surface of the water needs 0.10s to take evasive action. A pelican 25.0m above the water starts its dive. The fish first notices the pelican when the pelican is 5.0m above the water.
Does the pelican go hungry, or does it catch its prey?

An object starts from rest and travels in a straight line for 5s with a uniform acceleration of 4ms^-2. It continues to move with the uniform velocity acquired for a further 12s and it is finally brought to rest with a deceleration of 2.5 ms^-2.
Calculate the distance travelled and the time taken.

Thanks!

im confused........

[mark_alec]

For the first one, use the constant acceleration formula. You can calculate the velocity of the pelican after it has fallen 20 metres, and based on that, can work out how long it will take to travel the next 5, and whether that is greater than or less than 0.10 seconds.

For the second one, draw a velocity/time graph, the area underneath gives you the displacement.

[azn ho]

Thanks mark, for the second question i did draw a velocity time graph (which is part b of the question) to find the distance travelled and the time taken but i've been having trouble calculating it (which is part a of the question).

[mark_alec]

You should be able to break up the area under the graph into two triangles and one rectangle. The area of a triangle is 1/2 base*height. The time taken can be read off the graph (it will be when the velocity is zero).

[azn ho]

Thanks for your help, sorry what i was trying to say was i already worked it out graphicallly but i had trouble using equations to solve it, but i figured it out now.

[hard]

nice name azn ho

[azn ho]

Thanks 

[Flaming_Arrow]

sarcasm noted.