Homework Help: Physics Homework

Posted by Soly on Tuesday, September 11, 2007 at 10:05pm.

Could you please check my answers? Thanks!

1. You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn’t this mean the forces cancel one another, making acceleration impossible? Why or why not?

-No, because in order to accelerate the car, you have to have that interaction between you and the car.

2. If you stand next to a wall on a frictionless skateboard and push the wall with a force of 30N, how hard does the wall push on you? If your mass is 60 kg, what is your acceleration?

30 N

a=f/a
a=60kg/30 N = 2 kg/n

3. When a rocket engine is above the Earth’s atmosphere, what does it push on to cause acceleration?

-The rocket engine when above the Earth’s atmosphere the rocket pushes on Earth’s atmosphere in order to accelerate.

5. A truck has a trailer attached. As the truck drives off it exerts a force on the trailer that tends to pull the trailer along. But, according to Newton's 3rd Law, the trailer exerts an equal and opposite force on the truck which tends to stop the truck. How, then, can the truck and trailer accelerate and drive off?

-The forces cancel out.

Physics Homework - bobpursley, Tuesday, September 11, 2007 at 10:14pm
On number one, the answer is no,but the reason you gave is wrong. The force pushing back on your hand is equal to the friction on the car plus mass*acceleration.

2.3 are wrong.
5 I dont agree that the pull back force tends to stop the truck at all. Think some more on it.

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