Newton's Laws 1

Correct = C                          

There is no air resistance (frictional forces) acting on falling bodies in a vacuum. As a result a light body (for instance a feather) and a heavy body (for instance a coin) would fall with the same acceleration, hence the acceleration is independent of the mass of a body in a vavuum.

Correct = A 

$\text{Gravitational Force} = \text{km}_1 · \text m^2/r^2.$ If distance is doubled the term under the division line becomes $1/4 (1/2 \times 1/2 = 1/4).$ As a result, the gravitational force between the asteriods becomes a $1/4$ of its original value.

Correct = C

Application of Newton 3: actio = reactio, accordungly the spring balance will measure $20\; \text N.$

Correct = B 

No acceleration, hence $F = ma$ is zero. The only acting force on the bucket is the force of gravity (weight) which equals $250\; \text N.$

Correct = D

Again Newton 3: if a body $A$ exerts a force $F$ on a body $B,$ then body $B$ exerts an equal but opposite force on body $A.$ Only in option D the forces are equal (in magnitude is missing).

Correct = B 

Mass stays the same wherever you are, $2\; \text{kg}$ on the moon will be $2\; \text{kg}$ on the earth. However the force of gravity on earth is stronger, $2\; \text{kg}$ will experience a gravitational pull of $20\; \text N,$ hence option B.

Correct = D

At point $D$ the weight of all objects is acting: $\text{weight} = \text {mass (kg)} \times 10 \text{(N/kg)} = 13.5 \times 10 = 135\; \text N.$

Correct = B 

At rest the object weighs $200\; \text N,$ the weight decreases by $10\; \text N$ due to acceleration $(F = ma),$ only on accelerating downwards (option B) the weight decreases.

Correct = B 

Block is moving at constant speed hence acceleration is zero. Zero acceleration means frictional force is equal to pulling (or applied) force $F.$

Correct = A

Newton 1, also known as the law of inertia: a body will remain at rest or continue with constant velocity unless acted upon by an external resultant force.