Calculating the net force given velocity, acceleration and a frictional force.

Question

A 1t car initially travelling at 60kmh^-1 experiences a force of 1000N from the engine, and a frictional force of 130N in the opposite direction.

A) Calculate the net force on the car.

B) If the car accelerates for 4 seconds, calculate the final velocity of the car.

Answer 1

Net forward force = force of engine - frictional force; F = 1000 - 130 = 870 Newtons

 

from Newtons second law; Net Force = mass * acceleration

 

A) 870 = 1000 * a ; therefore a = 0.87 m/s^2

 

in 4 seconds its speed would have increased by 0.87 * 4 = 3.48 m/s

 

converting m/s to km/h; 3.48 * 3600/1000 = 12.53 km/h

 

B) Therefore final velocity after 4 seconds V = u + at = 60 + 12.53 = 72.53 km/h