Question

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s2 by means of a rope. The force of the block on the Earth is: A. 35 N, down B. 35 N, up C. 14 N, down D. 14 N, up E. 49 N, up

Answer 1

When the body touches the ground two types of Forces will be generated. The Force product of the weight and the Normal Force. This is basically explained in Newton's third law in which we have that for every action there must also be a reaction. If the Force of the weight is pointing towards the earth, the reaction Force of the block will be opposite, that is, upwards and will be equivalent to its weight:

F = mg

Where,

m = mass

g = Gravitational acceleration

F = 5*9.8

F = 49N

Therefore the correct answer is E.

Answer 2

Answer:

The force of the block on the Earth is 35N down.

Explanation:

Given data:

The mass of block is, $m=5\; \rm kg$.

Magnitude of downward acceleration is, $a=2.8\: \rm m/s^{2}$.

According to the Newton's Third Law of motion, "When some magnitude of force is applied by block on Earth in downward direction, then Earth will also apply same magnitude of force on Block, but in upward direction".

Therefore,

Force by block on Earth = Force by Earth on block

$F_{1} = - F_{2}$

Here, negative sign shows the upward direction of force by Earth on block.

$F_{1} = - m(a-g)$

Here, g is gravitational acceleration and its value is $9.8 \; \rm m/s^{2}$.

Solving as,

$F_{1} = - 5(2.8-9.8)\\F_{1} = 35\;\rm N \; (Downward)$

Thus, the magnitude of force by block on Earth is 35 N, down.

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