# physics

posted by .

A 450 g block is at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.670, and the coefficient of kinetic friction is 0.380. A force of magnitude P pushes the block forward and downward as shown in the figure below. Assume the force is applied at an angle of 39.0° below the horizontal.

(a) Assuming P is large enough to make the block move, find the acceleration of the block as a function of P. (Use P as necessary and round numbers to the third decimal place.) (b) If P = 6.81 N, find the acceleration and the friction force exerted on the block.
a = m/s2
Ffriction = N

(c) If P = 13.62 N, find the acceleration and the friction force exerted on the block.
a = m/s2
Ffriction = N

(d) Describe in words how the acceleration depends on P.

• physics -

Wb = mg = 0.45kg * 9.8N/kg = 4.41N. =
Weight of block.

Fb = (4.41N,0deg.).
Fp=Fh = 4.41sin(0) = 0 = Force parallel
to hor. surface.
Fv = 4.41cos(0) = 4.41N. = Force perpendicular to hor. surface.

Ff = u*Fv = 0.67 * 4.41 = 2.95N. = Force of static friction.

Ff = u*Fv = 0.360 * 4.41 = 1.59N. = Force of kinetic friction.

a. P must overcome the static friction to move the block:
Pcos39 - Ff = 0,
Pcos39 = Ff,
Pcos39 = 2.95,
P = 2.95 / cos39 = 3.8N. = Force applied.

When block starts to move, P must overcome kinetic friction to accelerate:
Fn = Pcos39 - Ff = 2.95 - 1.59 = 1.36 = Net force.

a = Fn / m = 1.36 / 0.45 = 3.03m/s^2.

b. Fn = 6.81cos39 - 1.59 = 3.7N.
a = Fn / m = 3.7 / 0.45 = 8.23m/s^2.

c. Fn = 13.62cos39 - 1.59 = 8.99N.
a = 8.99 / 0.45 = 19.98m/s^2.

d. Increasing P causes an increase in the net force, and the acceleration is proportional to the net force(a=Fn/m).

## Similar Questions

1. ### Physics/Math

A 17 N horizontal force F pushes a block weighing 6.0 N against a vertical wall. The coefficient of static friction between the wall and the block is 0.68, and the coefficient of kinetic friction is 0.48. Assume that the block is not …
2. ### Physics

A force of 40 N is applied at an angle of 30oabove the horizon to a 5 kg block that is at rest on a rough horizontal surface. After the block starts to move with an acceleration of 3 m/s2, what is the coefficient of kinetic friction …
3. ### physics

A 450 g block is at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.670, and the coefficient of kinetic friction is 0.380. A force of magnitude P pushes the block forward and …
4. ### Physics

A block of mass m1 is on top of a block of mass m2. Block 2 is connected by an ideal rope passing through a pulley to a block of unknown mass m3 as shown. The pulley is massless and frictionless. There is friction between block 1 and …
5. ### physics

A block M1 of mass 16.5 kg sits on top of a larger block M2 of mass 26.5 kg which sits on a flat surface. The kinetic friction coefficient between the upper and lower block is 0.425. The kinetic friction coefficient between the lower …
6. ### physics

4 kg block rests on a smooth horizontal surface,upper surface of 4 kg is rough.A block of mass 2 kg is placed on its upper surface.The acceleration of upper block with respect to earth when 4 kg mass is pulled by a horizontal force …
7. ### Physics

A block M1 of mass 13.0 kg sits on top of a larger block M2 of mass 23.0 kg which sits on a flat surface. The kinetic friction coefficient between the upper and lower block is 0.440. The kinetic friction coefficient between the lower …
8. ### Science

A Block rests on a horizontal surface.The normal force is 20 N.The coefficient of static friction between the block and the surface is 0,40 and the coefficient of dynamic friction is 0,20. What Is the magnitude of the frictional force …
9. ### physics

A block with a mass of 4.25 kg is placed at rest on a surface inclined at an angle of 44.8° above the horizontal. The coefficient of static friction between the block and the surface is 0.520, and a force of magnitude \$F\$ pushes upward …
10. ### Physics

A block M1 of mass 20.0 kg sits on top of a larger block M2 of mass 30.0 kg which sits on a flat surface. The kinetic friction coefficient between the upper and lower block is 0.415. The kinetic friction coefficient between the lower …

More Similar Questions