6-At time - 0 a 2-kg par title has a velocity of (4 m/s) I - (3 m/s) j. At t - 3

Question

6-At time - 0 a 2-kg par title has a velocity of (4 m/s) I - (3 m/s) j. At t - 3 s its velocity is (2 m/s) t + (3 m/s)j. What was the work done on it during this time? 7-A 1.5 kg crate falls from a height of 2.0 m onto an industrial spring scale with a spring constant of 1.5 x 10^5 N/m. Find the reading on the scale at its greatest compression. 8-A projectile of mass 0.50 kg is fired with an initial speed of 10 m/s at an angle of 60degree above the horizontal. Find the potential energy of the projectile-Tartu system when the projectile is its highest point (relative to the potential energy when the projectile is at ground level).

Explanation / Answer

4. N - mgcos30 = 0

N = mgcos30

and fmax = us N = 0.50 mgcos30

Fapp = mgsin30 - 0.50mgcos30 = 5 * 9.8 ( sin30 - 0.5cos30)

Fapp = 3.28 N

5. Ncos@ = mg and Nsin@ = mv^2/R

tan@ = v^2 / Rg = 12^2 / (50 * 9.8) = 0.294

@ = 16.4 deg

6. at t = 0

speed, v = sqrt(4^2 + 3^2) = 5 m/s

at t- 3 sec

v = sqrt(2^2 + 3^2) = 3.61 m/s

Using workenergy theorem,

work done = change in KE

W = 2 ( 3.61^2 - 5^2)/2 = - 12 J

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