mech 1: nonlinear motion and resultant force

State the resultant force, acceleration, velocity:

L = W, T = D

L is less than W

T is less than D

Lift weight thrust drag

Zero resultant force, zero acceleration, constant velocity

Resultant force facing down, Acceleration Decreasing, downward curve motion

Resultant force facing right, acceleration facing right, slows down in a level flight

If a luggage is 200 N but on a weighing scale it is shown as 180 N what is the scale doing?

If the force has decreased from its original size, the scale is technically moving upwards therefore decreasing velocity

What’s the equation for resultant force/how would you change acceleration?

F =ma

You can use three out of the four suvat equations

Newton definition and what is another type of unit you can use instead of newtons

The resultant force which will cause one kg mass to accelerate one metres/ second² in the direction of the force

N=kgms^-2

Weight definition

the gravitational force acting on the object

What are the equations for thrust/tension?

T=Fr+W

T=m(g+a)

How to calculate tension of the rope of one vehicle pulling the other with a resistive force

T - R=ma

The mass must be the object being pulled

Frictional force definition and causes

Force the opposes motion

Contact friction between two solids or fluid friction like drag due to the collisions with the molecules of the fluid

What are different factors that might affect drag?

Speed, surface area, aerodynamics, surface texture, viscosity, temperature

How do you calculate drag?

Fv²

Why can’t we predict the velocity in the future using the equations of motion?

Let’s see if the car accelerating, the velocity increases therefore drag increases however resultant force will decrease due to this. That means the acceleration will slowly decrease within time therefore not constant.

What does it mean in a question when it says fuel being used up?

This means the acceleration has increased

Terminal velocity definition

When the resultant force acting on a falling object through a fluid is zero, the velocity is constant

What does it mean when it says at a time before reaching terminal velocity?

This means before the weight is equivalent to the resultant force so it would be between initially zero and the weight

If you’re trying to calculate something, how would you calculate the angle if the angle isn’t given but the sides are

Use soh cah toa And substitute the sides

How to determine the term velocity of the skydiver with a mass or 75 kg and resist the force due to given by 0.24v²

Since resistive force is upwards and weight is going downwards

Weight + Fr=0.24v²

Rearrange

An accelerating car of mass 850 kg experience a forward driving force of 2.4kN. That particular moment in time velocity is 22 m/s. Calculate the instantaneous acceleration of the car given that the relationship between the drag force and the velocity is given as D=0.45v²

First calculate drag force (0.45)(22)²

Driving force minus drag since they are opposite direction

F=ma so that Fr/mass to get acceleration

What force wouldn’t happen when acting on a ladder?

Frictional force between the ladder and ground is unchanged

An airplane is in level flight at a constant velocity. The net force on the aircraft is equal to….

The resultant force equals zero since the velocity is constant. All forces acting on the object has the same magnitude.

On a rollercoaster ride the track descends vertically by 60 m whilst moving along 125 m of track. A courage of mass 450 kg start from rest and reaches the bottom of the descent with the speed V Having been subjected to an average frictional force of 750 N during the descent. What is the speed of the bottom of the descent?

Calculate their initial speed Wsin(o/h)

SUVAT using that initial ,final velocity of 0 and acceleration being 9.81 to find the time

Then use SUVAT using a distance of hypotenuse,initial velocity and time to calculate final velocity

If all effects of friction and air resistance have been eliminated and the acceleration due to gravity is constant, the value of the acceleration of the trolley can be doubled by…

Doubling the sine of the angle of the slope to the horizontal

A mass of 2.5 kg is released from rest at X and slides down a ramp of height 3m, hypotenuse of 5m and length of 4m to point Y.

When the mass reaches Y at the bottom of the ramp it has a velocity of 5 m/s. What is the average between the mass and the ramp?

first calculate the acceleration using a displacement of the hypotenuse, initial of 0m/s, final as 5m/s

Parallel component of speed is Wsin theta, sin theta is opposite over hypotenuse so 3/5

Fr= Wsin theta -ma

(2.5 × 9.81 × 3/5) - (2.5 × 2.5)

A safety test with a car of 650 kg travels at 15 m/s hit A wall. The front 22 m of the car crumples as the car is brought to a stop. what is the average force on the car during impact?

Use suvat to calculate the time using the horizontal components of distance, initial velocity, final velocity of 0 and acceleration being 0

Since acceleration=velocity/time. 15/time calculated

Average force= m(g+a)

How are two ways of calculating average frictional force

One is Ep=Ek+Wd then rearrange however the question asks or

First calculate the vertical component of acceleration. Then use mg sin theta - Fr=ma