# What horizontal force is required to accelerate the block

1. Jul 17, 2010

### a7med2009

A block of mass 4.0kg rests on a horizontal surface. What horizontal force is required to accelerate the block at 5.0m/s2 if the coefficient of kinetic friction is 0.25?

2. Jul 17, 2010

### graphene

Re: help :(

& any equations you may know that you think would be useful here.

3. Jul 17, 2010

### a7med2009

Re: help :(

ΣF=ma

Fk=mu * N

4. Jul 17, 2010

### a7med2009

Re: help :(

ma=4.0kg*5.0m/s^2
=20 N
Fk= 0.25 * 20
= 5 N

Is it correct???

5. Jul 18, 2010

### graphene

Re: help :(

so, how much force do you need to apply in order to overcome the frictional force?

6. Jul 28, 2010

### a7med2009

Re: help :(

ΣF=F-fk=mg
F=mg-fk
=(4.0)*(9.8)-(0.25)(39.2)
=29.4 N

7. Jul 28, 2010

### merryjman

Re: help :(

In your last post, you've got a vertical force (mg) and a horizontal force (fk) in the same equation. Not allowed.

In your previous post, you found the frictional force's maximum value. You also found that in order to accelerate at 5m/s/s, you need 20 Newtons of NET force.

So how much TOTAL force must be applied (horizontally) to overcome friction and give the block enough force to accelerate?

Last edited: Jul 28, 2010
8. Jul 28, 2010

### a7med2009

Re: help :(

ohh 0_o

it's
ΣF=F-fk=ma
F=ma+fk
=(4.0)*(5)+(0.25)(39.2)
=20+9.8
=29.8 N

9. Jul 28, 2010

### merryjman

Re: help :(

looks correct to me