Question

7. Find the specific gravity, weight density, and volume of the unknown object if it

weighs 40 Ib in air and 30 Ib in water.

2. A 10,000 kg vehicle will round the having a radius of 150 meter. The curved road is

banked at 25 degrees with the horizontal, find the minimum coefficient of friction.

4. Find the acceleration and the centripetal force of a 14 kN car that rounds the curved

of radius of 50 meters having a speed of 8 km/h.

5. Two perfectly elastic balls, weighing 27 N and 18 N, approach each other with a

speed of 6 m/s and 11 m/s, respectively. What is the speed of the balls after the

collision?

Answer 1

7. $40\ lb=178\ N$ ; $30\ lb=133\ N$

Specific gravity $SG=\rho_{object}/\rho_{water}=178/133=1.34$

Density $\rho=1.34\cdot1000=1340\ (kg/m^3)$

$V=178/(1340\cdot9.8)=0.014\ (m^3)$

2. Suppose that $v=5\ (m/s)$ . So, we have

$\mu=\frac{-v^2\cos25°+gR\sin25°}{v^2\sin25°+gR\cos25°}=\frac{-5^2\cdot\cos25°+9.8\cdot 150\cdot\sin25°}{5^2\cdot\sin25°+9.8\cdot150\cdot \cos25°}=0.45$

4. $a=v^2/r=2.22^2/50\approx0.1\ (m/s^2)$ and $F=ma=(14000/9.8)\cdot0.1=141\ (N)$

5. $v_1=\frac{m_1-m_2}{m_1+m_2}u_1+\frac{2m_2}{m_1+m_2}u_2=\frac{2.8-1.8}{2.8+1.8}\cdot 6+\frac{2\cdot 1.8}{2.8+1.8}\cdot 11=$

$=9.91\ (m/s)$

$v_2=\frac{2m_1}{m_1+m_2}u_1+\frac{m_2-m_1}{m_1+m_2}u_2=\frac{2\cdot 2.8}{2.8+1.8}\cdot 6+\frac{1.8-2.8}{2.8+1.8}\cdot 11=$

$=4.91\ (m/s)$