A2L: Assessing-to-Learn Physics

Meta-Information

Description: 

Determine the friction force on a slab from graphical information.

Goal: 

Problem solving

Level: 

Undergraduate

Keywords: 

Dynamics

Keywords: 

Forces

Keywords: 

Friction

Keywords: 

Mechanics

Keywords: 

Newton's Third Law

Source: 

UMPERG-ctqpe44-46

A block slides along a frictionless surface and onto a slab with a rough surface. The plot on the right shows the velocity of the blue slab as a function of time. The slab has mass of 4kg and the block has mass of 2kg. What is the friction force on the small block at t = 1 second?

1. 0.5 kg-m/s²
2. 0 kg-m/s²
3. 1 kg-m/s²
4. 4 kg-m/s²
5. 2 kg-m/s²
6. None of the above
7. Cannot be determined

Commentary

Answer

(5) The acceleration of the slab can be found from the plot. The only force on the slab in the horizontal direction is the friction force so it must be responsible for the acceleration. The force on the block can then be found using the 3rd law.