Posted by **Maggie** on Thursday, March 29, 2012 at 4:29pm.

Each of the four wheels of a car push on the road with a force of 4.0*10^3 N [down]. The driving force on the car is 8.0*10^3 N [W]. The fictional resistance on the car is 6.0*10^3 [E]. Calculate the following

A) the mass of the car

B) the net force on the car

C) the cars acceleration

The answers are

A) 1.6*10^3 kg

B) 2.0*10^3 N [W]

C) 1.2m/s^2

I just don't understand how to get these correct answers

- physics -
**Elena**, Thursday, March 29, 2012 at 5:48pm
M•g =4•m•g= 4•4•10^3 N

M = 4•4•10^3/9.8 =1.63•10^3 kg

There are 4 forces: Mg (downwards), normal force N ( upwards), driving force(to the left), and resistance force (to the right) . Net force is their sum.

Since N=Mg, net force is 8•10^3 – 6•10^3 = 2•10^3 N (to the left).

Acceleration = net force/mass =2•10^3/1.63•10^3 = 1.23 m/s^2

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