How to Solve Basic Physics Problems: Tension, Force, and Acceleration

[Raza]

Hello,
Just couple of of Physics questions. I want to make sure I got them right.

1.How much force (tension must a rope withstand if it is used to accelerate a 1700 kg car at 0.50m/s^2 on a frictionless surface.
I got:
$$(1700)(0.50)$$

$$F=850\frac{kgm}{s^2}$$

2.A 0.15kg baseball traveling at 35.0m/s strikes the catcher's mitt which recoils backwards 10 cm as it brings the ball to rest.
A) What was the force applied by the ball on the glove?
$$(0.15)(35)$$
$$F=5.25\frac{kgm}{s^2}$$
B) What was the force applied by the glove on the ball?
I don't know how to do this one

3.A parachutist is moving downward with a force due to gravity of 630N experience a a fricitonal air resistance of 450N.
A)Calculate the acceleration of the parachutist.
$$630-450=180M(Down)$$
B)Calclation the acceleration of the block.

$$A=\frac{F}{M}$$

$$F=(M)(G)$$

$$180=(M)(9.8)$$

$$M=\frac{180}{9.8}$$

$$M=18.36$$

$$A=\frac{180}{18.36}$$

$$A=9.8$$

 

[vsage]

I don't like the last two. For the third you are right up until F = MG where you for some reason assume the mass is variable with force as opposed to the acceleration. For #2, use the fact that $$v_f^2 = v_i^2 + 2ad$$ to find the acceleration. From there it's trivial to find the force.

 

[maverick280857]

I don't like the last two.

What do you mean you don't like them??

Anyway Raza, for question 2(b) you need to know Newton's Third Law: the magntiude force $$F_{AB}$$ on A due to B equals the magnitude of the force on B due to A, $$F_{BA}$$ and these forces are equal and opposite:

$$\vec{F_{AB}} = -\vec{F_{BA}}$$

Hope that helps.

Cheers
Vivek