1) When the friction less system shown above is accelerated by an applied force of magnitude the tension in the string between the blocks is (A) 2F (B) F (C) 2/3 F (D) 1/3 F 2) A block of mass 5 kilograms lies on an inclined plane, as shown below. The horizontal and vertical supports for the plane have lengths of 4 meters and 3 meters, respectively. The coefficient of friction between the planeand the block is 0.3. The magnitude of the force F necessary to pull the block up the plane with constant speed's most nearly (A) 30 N (B) 42 N (C) 49 N (D) 50 N
3 )The position of a toy locomotive moving on a straight track along the x-axis is given by the equation x = t3-6t2+ 9t, where x is in meters and t is in seconds. The net force on the locomotive is equal to zero when t is equal to (A) zero (B) 2 s (C) 3 s (D) 4 s
What is the acceleration of the block? (A) F/m (B) (Fcosφ)/m (C) (F-f)/m (D) (Fcosφ-f)/m

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

the only real purpose of sputnik 1 was to beat the us into space. we were getting close to launching a useful satellite, explorer 1 - which launched on january 31, 1958. the ussr had to beat that, so they launched sputnik 1 on october 4, 19