Mechanics questions | form five Physics

1. Why does the kinetic energy of an earth satellite change in the elliptical orbit?
2. Give two factors which determine whether a planet has an atmosphere or not.

A spacecraft is launched from the earth to the moon. If the mass of the earth is 81 times that of the moon and the distance from the centre of the earth to that of the moon is about 4.0×10​^5​ km;

1. Draw a sketch showing how the gravitational force on the spacecraft varies during its journey.
2. Calculate the distance from the centre of the earth where the resultant gravitational force becomes zero.

1. Justify the statement that ‘If no external torque acts on a body, its angular velocity will not be conserved’.
2. A car is moving with a speed of 30 ms​^-1 on a circular track of radius 500m. If its speed is increasing at the rate of 2ms^​-2​ ; find its resultant linear  acceleration.

An object of mass 1kg is attached to the lower end of a string 1m long whose upper end is fixed and made to rotate in a horizontal circle of radius 0.6m. If the circular speed of the mass is constant, find the;

1. Tension in the string.
2. Period of motion.

A 75kg hunter fires a bullet of mass 10g with a velocity of 400ms​^-1 from a gun of mass 5kg. Calculate the;

1. Recoil velocity of the gun.
2. Velocity acquired by the hunter during firing.

A jumbo jet travelling horizontally at 50ms^​-1 at a height of 500m from sea level drops a luggage of food to a disaster area.

1. At what horizontal distance from the target should the luggage be dropped?
2. Find the velocity of the luggage as it hit the ground.

The equation of simple harmonic motion is given as ​ x = 6sin10πt + 8cos10πt, where ​ x is in centimeter and ​ t ​ in second. Determine the;

1. Amplitude.
2. Initial phase of motion.

1. Show that the total energy of a body executing simple harmonic motion is independent of time.
2. Find the periodic time of a cubical body of side 0.2m and mass 0.004kg floating in water then pressed and released such that it oscillates vertically.

1. Mention two characteristics of projectile motion.
2. If the range of the projectile is 120​ m and its time of flight is 4sec,  determine the angle of projection and its initial velocity of projection assuming that the acceleration due to gravity ​ g ​ = 10ms^​-2​ .

1. State the principles on which the rocket propulsion is based.
2. A jet engine on a test bed takes in 40​ kg of air per second at a velocity of 100​ ms^-1 and burns 0.80​ kg of fuel per second. After compression and heating the exhaust gases are ejected at 600​ ms^-1​ ​ relative to the aircraft. Calculate the thrust of the engine.