Question

A truck with a mass of 1.5 x 103 kg accelerates to a speed of 18.0 m/s in 12.0 s from a dead stop. Assume that the force of resistance is a constant 400.0 N during the acceleration. What is the average power developed by the truckÍs engine?

Answer 1

There are several information's already given in the question. Based on those information's the answer can be easily deduced.
Mass of the truck = 1.5 x 10^3 kg
Constant force of resistance = 400 N
Final Velocity = 18 m/s
Initial velocity = 0 m/s
Time taken = 12 s
Then
Acceleration = (Final velocity - initial velocity)/Time
                     = 18 /12
                     = 3/2
                     = 1.5 m/s^2
Then
Driving force = Mass * Acceleration
                     = 1.5 * 10^3 * 1.5
                     = 2250 N
So
Net Force = 2250 - 400
                 = 1850 N
Average power developed = 1850 * 18
                                           = 3.33 * 10^4 W

Answer 2

Power = Net Force x velocity
Net force = driving force - force of resistance
Driving force = mass x acceleration
Acceleration = (final velocity - initial velocity) / time
Acceleration = (18 - 0) / 12 = 1.5 m/s²
Driving force = 1.5 x 10³ x 1.5
= 2250 N
Net force = 2250 - 400
= 1850
Power = 1850 x 18
= 3.33 x 10⁴ Watts