The horizontal surface on which the objects slide is frictionless.If M = 1.0 kg and the magnitude of the force of the small block on the large block is 5.2 N,determine F.
A)6.0 N
B)9.0 N
C)7.8 N
D)4.8 N
E)4.1 N

Question

The horizontal surface on which the objects slide is frictionless.If M = 1.0 kg and the magnitude of the force of the small block on the large block is 5.2 N,determine F. 
A)6.0 N 
B)9.0 N 
C)7.8 N 
D)4.8 N 
E)4.1 N

Quizplus · Accepted Answer

Since the horizontal surface on which the objects slide is frictionless, the acceleration experienced by both the blocks must be the same. Using Newton's second law:
F = Ma 
where F is the force of the small block on the large block, M is the mass of the large block and a is the acceleration of both blocks. Since both blocks have the same acceleration, we can solve for a using only the mass of the large block: 
a = F/M 
Using the given values: 
a = 5.2/1.0 = 5.2 m/s^2 
Now, we can use this acceleration to solve for the force F needed to move the large block:
F = Ma 
F = 1.0 kg x 5.2 m/s^2 = 5.2 N 
Therefore, the force F needed to move the large block is 5.2 N. However, the problem is asking for the magnitude of the force of the small block on the large block, which is also 5.2 N since the two forces are equal and opposite according to Newton's third law. Thus, the answer is C (7.8 N is not a correct choice).

The Horizontal Surface on Which the Objects Slide Is Frictionless