Need help with physics questions?

Posted on 2014-12-08 08:19:00 in Physics by LEON

I don't have an answer key to the exams so I do not know if my answers are correct.

3. Two cars travel down a straight segment of freeway in adjacent lanes in the same direction. Car A starts from rest with an acceleration of 4.50 m/s^2 while car B starts at the same time a distance of 12.5 m ahead of car A with an initial speed of 35 m/s and an acceleration of -2.50 m/s^2. Find when and where these two cars will meet next to each other.

4. An object initially at rest experiences a time dependent acceleration of a(t)=1.50t^2. Find the acceleration, velocity, and displacement of the object at t=3.33s.

For acceleration I plugged in t=3.33s in a(t) and got 16.6 m/s^2.
For Velocity I took the anti derivative of a(t) and plugged in t=3.33s to get 18.5 m/s
For displacement I took the second anti derivative of a(t) and plugged in t=3.33s to get 15.4m.
I do not know if I am doing this right since there are so many equations for physics.

5. A rock released from rest at a height H reaches the ground in 3.5s. Determine H and find the velocity of the rock as it is at half of its original height. Ignore Air Resistance.

To find H I used x=(.5)(a)(t^2) with a=9.8m/s^2 and t=3.5seconds to get 60m.
Based on my first answer of 60 meters, half of that would equal 30 meters. Using the same equation with a =9.8m/s^2 and x=30 m to get t=2.47 seconds. I then assumed that it took 2.47 seconds to reach half of its height so I used v=x/t to get a velocity of 12.1m/s.

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