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In Fig. 6-33, two blocks are connected over a pulley. The mass of block A is10kg , and the coefficient of kinetic friction between A and the incline is 0.20 . Angle ฮธ of the incline is 30ยฐ . Block A slides down the incline at constant speed. What is the mass of block B? Assume the connecting rope has negligible mass. (The pulleyโ€™s function is only to redirect the rope)

Short Answer

Expert verified

The mass of block B is3.3kg

Step by step solution

01

Given

Mass of block is A, mA=10kg

Coefficient of kinetic friction between the incline and Body A,ฮผk=0.20

Angle of incline, ฮธ=30ยฐ

02

Determining the concept

The problem is based on Newtonโ€™s second law of motion which states that the rate of change of momentum of a body is equal in both magnitude and direction of the force acting on it. To find the acceleration of the body A, use Newtonโ€™s 2nd law of motion.

Formula:

Fnet=โˆ‘ma

where, F is the net force, m is mass and a is an acceleration.

03

Determining the free body diagram

Free Body Diagram of the body A and body B:

04

Determining the mass of block B

Block A slides down the incline at constant speed.Thus, the acceleration of block A is 0.By using Newtonโ€™s 2nd law of motion along the vertical direction (along y) to the system,(positive x axis along the incline and the positive y along the vertical direction),

N=mAgcos30=0N=mAgcos30

Thus, the frictional force,

fk=ฮผkN=ฮผkmAgcos30

Now, applying Newtonโ€™s 2nd along horizontal direction to the Body A having massm,

T+fkโ€mAgsin30=0T+ฮผkโ€mAgsin30โ€mAgsin30=0 (1)Similarly, apply to the Body B having mass mโ€™,

mBg-T=0 (ii)

Adding equation (i) and (ii),

mAg+ฮผkmAgsin30โ€mAgsin30=0mB=mAsin(30)โ€ฮผkcos30=3.3kg

Therefore, the mass of block B is 3.3 kg.

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