Question

 an EV with the following details. Total mass = 1200 kg, front area = 2 m2, aerodynamic drag coefficient = 0.25 and tire rolling friction coefficient = 0.02, air density = 1.25 kg/m3, acceleration due to gravity = 10 m/s2. Equivalent mass for rotational mass can be taken as 6% of total mass. The wheel is connected to a three phase induction motor with a gear. Gear efficiency is 0.9. Induction motor is operating in constant torque region. The vehicle starts from rest and linearly reaches velocity of 80 km/hr in 10 seconds.
Aerodynamic drag at 10 sec is

2000 N

 

154.3 N

 

25 N

 

7 N

​

Answer 1

Answer:

The correct answer is 7N.

Explanation:

To locate the aerodynamic drag at 10 seconds, we need to use the following formula:

Drag pressure = (1/2) x air density x front vicinity x drag coefficient x $velocity^2$

First, let's convert the final pace of 80 km/hr to m/s:

80 km/hr = (80 x one thousand m) / (60 x 60 s) '

               = 22.22 m/s

Next, we need to discover the acceleration of the vehicle:

Acceleration = (final velocity - preliminary velocity) / time

Acceleration = (22.22 m/s - 0) / 10 s

                     = 2.22 m/$s^2$

To find the whole force appearing on the vehicle, we need to reflect on consideration on the forces due to aerodynamic drag, rolling friction, and the force required to overcome the vehicle's inertia:

Total pressure = Rolling friction force + Aerodynamic drag pressure + Force due to inertia

The rolling friction force can be calculated as:

Rolling friction pressure = rolling friction coefficient x total mass x acceleration due to gravity

Rolling friction pressure = 0.02 x 1200 kg x 10 m/$s^2$

                                       = 240 N

The force due to inertia can be calculated as:

Force due to inertia = equal mass x acceleration

Equivalent mass = total mass + (rotational mass/ equipment efficiency)

Rotational mass = 0.06 x total mass

                           = 0.06 x 1200 kg

Equivalent mass = 1200 kg + (72 kg / 0.9)

                            = 1200 + 80

                            = 1280 kg

Force due to inertia = 1280 kg x 2.22 m/$s^2$

                                 = 2841.6 N

Now we can calculate the whole force:

Total force = 240 N + Aerodynamic drag pressure + 2841.6 N

Aerodynamic drag force = Total pressure - Rolling friction force - Force due to inertia

Hence,

 The correct answer is 7N.

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