Question

A car of mass 1200kg starts from rest, accelerates uniformly to a speed of 4.0 meters per second in 2.0 seconds and continues moving at this constant speed in a horizontal straight line for an additional 10 seconds. the brakes are then applied and the car is brought to rest in 4.0 seconds. A constant resistance force of 500N is acting on the car during its entire motion.
a) Calculate the force accelerating the car in the first 2.0 seconds of the motion
b) Calculate the average power developed by the engine in the first 2.0 seconds of the motion
c) calculate the force pushing the car forward in the next 10 seconds
d) Calculate the power developed by the engine in those 10 seconds
e) Calculate the braking force in the last 4.0 seconds of the motion
f) Describe the energy transformations that have taken place in the 16 seconds of the motion of this car

Answer 1

a. F = m*a.

a = (V-Vo)/t = (4-0)/2 = 2 m/s^2.

F = 1200*2 = 2400 N.

b. d = 0.5a*t2.
d = 0.5*2*2^2 = 4 m.

P = F*d/t = 2400 * 4/2 = 4800 Joules/s.

Answer 2

1. A car starts from rest and accelerates at 3 m/s2 for 5 seconds and then continues with constant velocity. Calculate the distance covered in 15 seconds since it starts from rest.