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Newton Laws Dynamics without Friction

The Examples of High School Physics Problems and Solutions based on Indonesian Currriculum: Newton's Law part 1 (Grade 10). 

Problem 1
Two blocks connected by a light string from a frictionless pulley as figured below.



m1 = 4 kg dan m2 = 6 kg. Find :
a) the acceleration of each block
b) the tension in the string
c) the distance traveled by m2 for 2 sec
d) the distance between m1 and m2 for 2 sec
Use the acceleration due to gravity g = 10 m/s2

Solution
The first block acceleration (a1) and the second block acceleration (a1) are equal.
a) the acceleration
Free body diagram of first block :





Free body diagram of second block:


From eq I and eq II we find the acceleration:



b) the tension in the string (T)



c) the distance traveled by second block for 2 sec



d) for 2 sec the distance first and second block is 8 m.

Problem 2

A constant force F = 10 N acting on a block of 5 kg at an angle of 60° above the horizontal as shown below.



a) draw a free body diagram showing the all forces acting on the block
b) find the acceleration of the block
c) find the magnitude of normal force
Use the acceleration due to gravity g = 10 m/s2

Solution
a) the free body diagram, N = normal force, W = block weight, shown below:



b) the acceleration
Applying Newton's 2nd Law in the horizontal direction :



c) Normal force (N)
Applying Newton's Law in the vertical direction :



Problem 3
A block of 4 kg rests on the frictionless floor and block B of 6 kg connected by string running over a pulley. Neglect the mass of the string and the pulley friction.



Find:
a) the acceleration of A and B
b) the tension in the string
Use the acceleration due to gravity g = 10 m/s2

Solution
a) free body diagram of the block A (forces in horizontal direction)





Free body diagram of the block B







b) tension in the string



Problem 4
A system contains three block, massless string and frictionless pulleys shown below:



m1 = 1 kg, m2 = 2 kg dan m3 = 3 kg,
Find the accelaration of each block!
Use the acceleration due to gravity g = 10 m/s2

Solution
Newton's 2nd Law from first block, equation I



Newton's 2nd Law from second block, equation II



Newton's 2nd from third block, equation III



Note that a1, a2, a3:


equation IV

From eq. III and eq. IV



From eq. I and eq. II



From eq.V and eq. VI



From eq. II and eq. VII





Problem 5
Given a system contains A of 5 kg and B of 15 kg shown below:



Find the acceleration of B, assume the floor and the pulley are frictionless!
Use the acceleration due to gravity g = 10 m/s2

Solution

Free body diagram of A in traveling direction





Free body diagram of B in traveling direction





From eq I and II



 

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