Two horizontal forces, P and Q , are acting on a block that is placed on a table

Question

Two horizontal forces, P and Q , are acting on a block that is placed on a table. We know that P is directed to the left but the direction of Q is unknown; it could either be directed to the right or to the left. The object moves along the x-axis. Assume there is no friction between the object and the table. Here P = ?7.3 N and the mass of the block is 4.4 kg. (a) What is the magnitude and direction of Q when the block moves with constant velocity? (Indicate the direction with the sign of your answer.) N (b) What is the magnitude and direction of Q when the acceleration of the block is +6.1 m/s2. (Indicate the direction with the sign of your answer.) N (c) Find the magnitude and direction of Q when the acceleration of the block is ?6.1 m/s2. (Indicate the direction with the sign of your answer.) N

Explanation / Answer

Given:

Force P = - 7.3 N

Mass M = 4.4 kg

Solution

A)

if the velocity is constant then the acceleration is zero.

Acceleration = 0 m/s2

Net force F = P + Q

Ma = P + Q

4.4 x 0 = -7.3 +Q

0 = -7.3 + Q

Q = +7.3 N

B)

a = + 6.1 m/s2

F = P +Q

Ma = P + Q

4.4 x 6.1 = - 7.3 + Q

Q = +34.14 N

C)

a = - 6.1 m/s2

F = P +Q

Ma = P + Q

4.4 x (-6.1) = - 7.3 + Q

Q = -19.54 N

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