# Physics Prelab Questions

406 words | 2 page(s)

Question 1
According to Newton’s First law, a body will remain in a state of rest or uniform motion, unless it is acted upon by an external force (“S-Cool, the revision website). In this case, the mass is in an uniform motion which means that there is no acceleration. Since there is no acceleration, the body can be brought to rest in finite time. The friction force which can bring the box to rest must be equal to the applied force. Therefore in this case;
F_App=F_K
Where F_App is the applied force and F_K is the kinetic friction force. There exists a constant called the coefficient of kinetic friction, μ_k, such that;
F_App=μ_k F_K
However, when μ_k is equal to unity the object stops. Therefore, in this case, since F_App is 50N, then;
F_App=F_K=50N
The magnitude of the friction force is 50N
Since the friction force acts on the opposite direction (1800), the work done by the frictional force, W_Fric, is given by’
W_Fric=F_K×displacement×cos⁡θ
=50N×6m×cos⁡180=-300J
The force done by the applied force, W_App, is;
=50N×6m×cos⁡0=300J
Therefore, the net work done, W_Net, is;
W_Net 〖=W〗_App+W_Fric=-300J+300J=0J

Question 2
The Logger-Pro Force graph is changed from Force vs. Time to Force vs. Position since the work done on an object is obtained when there is a displacement produced by the force and not the time spent by the force on the object. Similarly, the change in kinetic energy of an object is equal to the work done by the object which also depends on the displacement of the object.

Question 3
Work is defined as the product of force and the displacement produced by that force in the direction of the force. The SI unit of work is joules (J).
Question 4
The change in kinetic energy in of the cart is equal to the work done by the hanging mass.
∆KE=W_Net
Therefore, the work done by the hanging mass is given by;
W_Net=mgh
Where g=9.81m/s^2.
Since m = 100g = 0.1kg and h = 1.5m then the work done will be;
W_Net=0.1kg×9.81m/s^2×1.5m
=1.4715J
But since
∆KE=W_Net then;
∆KE=1.4715J

References
• “S-Cool, the revision website.” Newton’s Laws | S-Cool, the revision website, www.s-cool.co.uk Accessed 1 Mar. 2017.