NEET Work Energy and Power — Set 5

Question 1

A spring ($ k = 900 \, \text{N/m} $) is stretched from $ 0.05 \, \text{m} $ to $ 0.1 \, \text{m} $. What is the work done by the spring force?

Accepted Answer

Work $ W_s = \frac{1}{2} k (x_i^2 - x_f^2) = \frac{1}{2} \times 900 \times (0.05^2 - 0.1^2) = 450 \times (0.0025 - 0.01) = -3.375 \, \text{J} $.

Question 2

A $ 9 \, \text{kg} $ block is pushed with $ 45 \, \text{N} $ over $ 7 \, \text{m} $ on a frictionless surface, starting from rest. What is its final speed?

Accepted Answer

Work $ W = 45 \times 7 = 315 \, \text{J} $. By work-energy theorem, $ K_f = W \Rightarrow \frac{1}{2} \times 9 \times v^2 = 315 \Rightarrow v^2 = 70 \Rightarrow v = \sqrt{70} \approx 8.37 \, \text{m/s} $.

Question 3

A $ 1.5 \, \text{kg} $ object is dropped from $ 16 \, \text{m} $. What is its speed just before hitting the ground? (Take $ g = 10 \, \text{m/s}^2 $)

Accepted Answer

Potential energy $ V = mgh = 1.5 \times 10 \times 16 = 240 \, \text{J} $. Kinetic energy $ \frac{1}{2} m v^2 = 240 \Rightarrow v^2 = 320 \Rightarrow v = \sqrt{320} \approx 17.89 \, \text{m/s} $.

NEET Physics: Work Energy and Power — Practice Set 5

Q1. A spring (\( k = 900 \, \text{N/m} \)) is stretched from \( 0.05 \, \text{m} \) to \( 0.1 \, \text{m} \). What is the work done by the spring force?

Q2. A \( 9 \, \text{kg} \) block is pushed with \( 45 \, \text{N} \) over \( 7 \, \text{m} \) on a frictionless surface, starting from rest. What is its final speed?

Q3. A \( 1.5 \, \text{kg} \) object is dropped from \( 16 \, \text{m} \). What is its speed just before hitting the ground? (Take \( g = 10 \, \text{m/s}^2 \))

Q4. A \( 50 \, \text{g} \) bullet moving at \( 400 \, \text{m/s} \) loses \( 75\% \) of its kinetic energy passing through a target. What is its emergent speed?

Q5. A \( 15 \, \text{kg} \) mass is lifted \( 6 \, \text{m} \) in \( 4 \, \text{s} \) at constant speed. What is the power? (Take \( g = 10 \, \text{m/s}^2 \))

Q6. A \( 4 \, \text{kg} \) block is pushed with \( 20 \, \text{N} \) over \( 6 \, \text{m} \) on a frictionless surface, starting from rest. What is its final speed?

Q7. A \( 0.8 \, \text{kg} \) object is dropped from \( 10 \, \text{m} \). What is its kinetic energy just before impact? (Take \( g = 10 \, \text{m/s}^2 \))

Q8. A \( 3 \, \text{kg} \) ball at \( 18 \, \text{m/s} \) collides elastically with a stationary \( 9 \, \text{kg} \) ball. What is the speed of the \( 3 \, \text{kg} \) ball after collision?

Q9. A \( 0.2 \, \text{kg} \) ball is dropped from \( 12 \, \text{m} \). What is its speed just before hitting the ground? (Take \( g = 10 \, \text{m/s}^2 \))

Q10. A \( 4 \, \text{kg} \) block slides down a frictionless incline from a height of \( 3 \, \text{m} \). What is its speed at the bottom? (Take \( g = 10 \, \text{m/s}^2 \))