A 10 kg block sits on a flat surface whose μs is 0.60 and whose μk is 0.40
a. What horizontal force is required to get the block move?
b.If we continue to apply the same force as in part (a) what will the blocks acceleration be???
http://www.jiskha.com/display.cgi?id=1346025140
What was it about this response did you not understand?
in the answer :
force=.6*mg to move
net force=ma
first force-.6mg=ma solve for a
what is the first force??... should i subtract it to .6mg?
thanks.
To find the horizontal force required to get the block to move, we need to use the concept of static friction. The equation for static friction is:
fs ≤ μs * N
where fs is the force of static friction, μs is the coefficient of static friction, and N is the normal force.
In this case, since the block is on a flat surface, the normal force N is equal to the weight of the block, which can be calculated as:
N = m * g
where m is the mass of the block and g is the acceleration due to gravity (approximately 9.8 m/s²).
a. To find the horizontal force required to get the block to move, we need to find the maximum static friction:
fs = μs * N
Substituting the values, we have:
fs = 0.60 * (10 kg * 9.8 m/s²)
fs = 0.60 * 98 N
fs = 58.8 N
Therefore, a horizontal force of at least 58.8 N is required to get the block to move.
b. Once the block starts moving, we need to consider kinetic friction. The force of kinetic friction is given by the equation:
fk = μk * N
where fk is the force of kinetic friction and μk is the coefficient of kinetic friction.
Using the same values for N as before, we can calculate the force of kinetic friction:
fk = 0.40 * (10 kg * 9.8 m/s²)
fk = 0.40 * 98 N
fk = 39.2 N
Since we are applying a horizontal force equal to the force of static friction (58.8 N), which is larger than the force of kinetic friction, the block will continue to accelerate. The acceleration can be calculated using Newton's second law:
F = m * a
where F is the net force acting on the block, m is the mass of the block, and a is the acceleration.
In this case, the net force is the difference between the applied force and the force of kinetic friction:
F = fk - fa
Substituting the values:
F = 39.2 N - 58.8 N
F = -19.6 N
Since the net force is negative (opposite to the direction of motion), the acceleration will also be negative, implying that the block will decelerate. Therefore, the block's acceleration will be -1.96 m/s².