Question

A car is moving at 65.0 km/h at a distance of 125 m from a traffic light when the light turns red. The weight of the car is 14800 N

(a) What is the mass of the car in kg?

(b) If the driver wishes to stop at the light, what is the required constant acceleration of the car in m/s^2

(c) What will be the velocity of the stone when it hits the water?

Answer 1

a)

$$m=\frac{W}{g}=\frac{14800}{9.8}=1510\ kg$$

b)

$$v^2=2as\\\frac{65^2}{3.6^2}=2(125)a\\a=1.30\frac{m}{s^2}$$

c)

$$F_f=ma=(1510)(1.3)=1960\ N$$