Friction and Ramps Quizizz

A 6 kg box is sitting at rest. It has a coefficient of static friction of 0.5 and of kinetic friction of 0.2

I push on it with 15 N. What is the acceleration of the box, m/s²?

Mathematical Equivalence

ON

Answer explanation

The maximum static friction is 30 N (normal force of 60 N multiplied by 0.5).

We did not push hard enough to break static friction, so the acceleration and the velocity are zero.

A 8 kg box is sitting at rest. It has a coefficient of static friction of 0.4 and of kinetic friction of 0.2

I push on it with 40 N. What is the acceleration of the box, in m/s²?

Mathematical Equivalence

ON

Answer explanation

The maximum static friction is 32 N (normal force of 80 N multiplied by 0.4).

We pushed hard enough to break static friction. SO the box will experience kinetic friction instead. Kinetic friction is 16 N (normal of 80 multiplied by 0.2).

So, if we have a push of 40 N and an opposing kinetic friction of 16 N, our next force is 24 N. Divide that by mass (8 kg) to get 3 m/s².

A 12 kg box is sitting at rest. It has a coefficient of static friction of 0.3 and of kinetic friction of 0.1

I push on it with 20 N. What is the acceleration of the box, in m/s²?

Mathematical Equivalence

ON

Answer explanation

The maximum static friction is 36 N (normal force of 80 N multiplied by 0.4).

We did not push hard enough to make the box move (acceleration and velocity remain zero).

A 12 kg box is sitting at rest. It has a coefficient of static friction of 0.3 and of kinetic friction of 0.1

I push on it with 60 N. What is the acceleration of the box, in m/s²?

Mathematical Equivalence

ON

Answer explanation

The maximum static friction is 36 N (normal force of 80 N multiplied by 0.4).

We broke static friction. Recalculate with kinetic friction!

Kinetic friction is 120 N (normal) multiplied by 0.1 (coefficient of kinetic friction) = 12 N

A push of 60 N and opposing friction 12 N results in 48 N as a net force. Divide that by mass for an acceleration of 4 m/s².

A box is being pushed across a rough surface and is traveling at a constant speed. What must be true?

• It is incurring static friction

• Net force is zero

• Kinetic friction is greater than applied force

• Applied force is greater than kinetic friction

If the net force is zero, then the object's velocity is...

• must be zero

• decreasing

• increasing

• not changing

A box is sliding up a rough ramp. What direction does friction point?

• Down the ramp

• Up the ramp

• Perpendicular to the ramp

• Both up and down the ramp at the same time

A box is sitting stationary on a rough ramp. What direct does the static friction point?

• Up the ramp

• Down the ramp

• Perpendicular to the ramp

• It doesn't have any static friction

A box of mass m is sliding down a frictionless ramp, set at an angle θ above the horizontal. What is the net force acting on the box?

• mgcosθ

• mgsinθ

• mg

• mgtanθ

I want to move a heavy couch across my nice wood floors. In order to reduce damage to my floors, I should ______ before I push the couch sideways.

• Push down into the couch to decrease the static friction

• Lift the couch as much as possible to reduce normal force

• Have my friend sit on the couch to change the coefficients