Since the force of friction is the only force acting on the box, according to Newton's second law its magnitude must be equal to the product between mass (m) and acceleration (a):

$F_f = ma$ (1)

We can find the mass of the box from its weight: in fact, since the weight is W = 50.0 N, its mass will be

$m=\frac{W}{g}=\frac{50.0 N}{9.8 m/s^2}=5.1 kg$

And we can fidn the acceleration by using the formula:

$a=\frac{v-u}{t}$

where

v = 0 is the final velocity

u = 1.75 m/s is the initial velocity

t = 2.25 s is the time the box needs to stop

Substituting, we find

$a=\frac{0-1.75 m/s}{2.25 s}=-0.78 m/s^2$

(the acceleration is negative since it is opposite to the motion, so it is a deceleration)

Therefore, substituting into eq.(1) we find the force of friction:

$F_f = (5.1 kg)(-0.78 m/s^2)=-4.0 N$

Where the negative sign means the direction of the force is opposite to the motion of the box.

6 0

3 years ago

When one "throws” a punch, the forearm applies force to the fist. Consider a(n) 0.75 kg fist that goes from rest to a

deff fn [24]

Formula for acceleration

6 0

3 years ago

At $.110 per kWh, what does it cost to leave a 40-W porch light on day and night for a year?

nlexa [21]

The cost of electricity be $ 38.544.

<h3>What is electricity?</h3>

Electricity is the passage of charges in a conductor. From one end of the terminal to the other, charges are transmitted. Usually, the terminal moves from positive to negative. Since the nucleus holds the electrons loosely, they can move freely throughout the body.

Watts are units of power used to measure electrical output.

Price of electricity is $ 0.110 per kWh .

If a 40-W porch light on day and night for a year, total amount of electricity spend = power of the bulb × time

= 40 W × 1 year

= 40 W × 365 day

= 40 W × 365 ×24 h

= 350400 Wh

= 350.4 kWh.

Hence, the cost of electricity be = $350.4 × 0.110 = $ 38.544.

Learn more about electricity here:

brainly.com/question/8971780

#SPJ1

4 0

1 year ago