Physics Mixed Problems 90591E
1. **Problem 1: Measurement and Dimensions**
State the problem: Given a physical quantity, find its dimensional formula.
Formula: Use the fundamental dimensions: Mass ($M$), Length ($L$), Time ($T$).
Example: Velocity has dimensions of length per time, so $[V] = LT^{-1}$.
Explanation: Dimensional analysis helps verify equations and convert units.
2. **Problem 2: Friction**
State the problem: Calculate the force of friction acting on a body.
Formula: $F_f = \mu N$, where $\mu$ is the coefficient of friction and $N$ is the normal force.
Explanation: Friction opposes motion; static friction prevents motion, kinetic friction acts during motion.
3. **Problem 3: Linear Momentum Conservation**
State the problem: Analyze a collision where two bodies interact.
Formula: Total momentum before collision equals total momentum after collision: $$m_1v_1 + m_2v_2 = m_1v_1' + m_2v_2'$$
Explanation: Momentum is conserved in isolated systems without external forces.
4. **Problem 4: Boat and Person Problem**
State the problem: A person walks on a boat; find the boat's displacement.
Formula: Using conservation of momentum and center of mass:
$$m_p x_p + m_b x_b = 0$$
Explanation: The boat moves opposite to the person to conserve momentum.
5. **Problem 5: Mechanical Energy Conservation**
State the problem: Calculate velocity of a body falling under gravity without friction.
Formula: Total mechanical energy conserved:
$$PE_i + KE_i = PE_f + KE_f$$
Example: $$mgh = \frac{1}{2}mv^2$$
Explanation: Potential energy converts to kinetic energy.
**Bonus Questions:**
6. **Bonus 1: Dimension Equation Building**
State the problem: Derive the dimensional formula for force.
Solution: Force = mass × acceleration
$$[F] = M \times LT^{-2} = MLT^{-2}$$
7. **Bonus 2: Friction and Inclined Plane**
State the problem: Find minimum angle for an object to start sliding on an inclined plane with friction coefficient $\mu$.
Formula: $$\tan \theta = \mu$$
Explanation: At this angle, component of gravity overcomes friction.
8. **Bonus 3: Elastic Collision in One Dimension**
State the problem: Find final velocities after elastic collision.
Formula:
$$v_1' = \frac{(m_1 - m_2)v_1 + 2m_2 v_2}{m_1 + m_2}$$
$$v_2' = \frac{(m_2 - m_1)v_2 + 2m_1 v_1}{m_1 + m_2}$$
Explanation: Both momentum and kinetic energy conserved.