Is the following statement true or false:

"If the instantaneous velocity of an object is zero, its acceleration must also be zero." Explain your answer.

A block of mass 50 kg is pulled horizontally on a floor. If the coefficient of kinetic friction between the block and the floor is what is the horizontal force required to pull it at a constant velocity? Draw the free-body diagram.

A stone is lodged in a rotating car wheel at a distance of 0·2 m from the axis of rotation. The average angular acceleration of the stone is 100 rad s-2. What will the stone's speed be after 2·0s?

If the free fall acceleration on the moon is measured to be 1·60 and its mass is 7·4 x 10^22 kg, what is its radius? =6·67 x 10^-11 Nm^2

Determine the potential energy function associated with the an harmonic spring force:



State the work-energy theorem. A fire-cracker of mass 0·10 kg is launched from rest. The work d0!1e on the fire-cracker by non-conservative forces due to burning fuel is 100 J. Calculate the speed of the fire-cracker when it reaches a height of 20 m. Neglect air resistance and the mass lost due to the burning of fuel.
Take g 10 ms^-2.

A boy of mass 20 kg stands at the edge of a merry-go-round having a moment of inertia 320 kg m2 and a radius of 4·0 m. The merry-go-round is initially at rest. The boy then starts to walk counter-clockwise around the edge of the merry-go-round at a constant speed of 2.0 ms^-l.

In what direction and with what angular speed does the merry-go-round rotate?

How much work does the boy do to set himself and the merry-go-round in motion?

A star moves in a circular orbit with a time period of 20 hours about another massive star whose mass is 2·0 x 10^30 kg. Use Kepler's third law to calculate the distance between the two stars.

Write down the expression for the centre of mass of an N-particle system. Three particles of equal mass are placed at the vertices of an isosceles right-angled triangle. Determine the centre of mass of the system.

A particle A of mass m collides elastically with another particle B of mass 4 m which is initially at rest. After the collision B moves at an angle e with the initial direction of motion of A. Determine the direction in which A moves after the collision. If the initial speed of A is determine the speeds of the two particles after the collision.

Two astronauts, each of mass 60 kg, are tied by a light rope and the distance between them is 10 m. They are isolated in space and orbiting their C.m. (centre of mass) at a speed of 6 ms^-1. Calculate the angular momentum and kinetic energy of the system. After a while they move closer to each other so that the distance between them is 5·0 m. What is the new angular momentum of the system? What are the new speeds? What is the kinetic energy of the system now?

A bird of mass 0·5 kg is flying due north at the latitude 300N at a speed of 2 ms^-1. Determine the Coriolis force acting on it in the Earth's rotating frame.

A child of mass m stands at rest in a lift moving downward with an acceleration 6 ms^-2. Determine the apparent weight of the child. Draw the free body diagram. Take g 9.8 ms^-2.