Average Speed and Force Question

[baltar]

Hello everyone! I am really terrible at physics.
I genuinely tried doing them(looking for similar examples in the book and such), but am still stuck. If someone could point me in the right direction, I'd appreciate it. Thanks in advance!

1) A car is making a 12 mile trip. It travels the first 8.0 miles at 30mph and the last 4.0 miles at 60mph. What is the car's average speed for the entire trip?
I got 40mph. This is what I did 0.66666(30) + 0.33333(60) = 40mph.


2) A car is moving with constant acceleration. At t = 5.0 its velocity is 8.0m/s and t=8.0s its velocity is 12.0m/s. What is the distance traveled in that interval of time?

3) To move a large crate across a rough floor, you push on it with a force F at an angle of 21 degrees below the horizontal. Find the force necessary to start the crate moving, given that the mass of the crate is 32 kg and the coefficient of static friction between the crate and the floor is 0.57

 

[Integral]

1. Use your knowledge of speeds and distance to compute the total time for the trip. Use that time and the total distance to get a average velocity.

2. and 3. Show us something of what you know about these situations.