Suppose you pushed a door at a point where the lever arm is I = 0.8 m. If the to

Question

Suppose you pushed a door at a point where the lever arm is I = 0.8 m. If the torque you caused was tau = 80 Nm, with what force did you push the door? (A) 0.01 N (B) 80 N (C) 64 N (D) 100 N Ball A is thrown horizontally, and ball B is dropped from rest from the same height at the same moment. Which of the following is true? (A) Ball B reaches the ground first (B) Ball A has the greater speed when it reaches the ground (C) Ball A reaches the ground first (D) B and C You apply torque when you ___ (A) open a door (B) use a wrench (C) turn a steering wheel (D) all of them Pascal's principle is based on conservation of ___ (A) energy (B) momentum (C) mass (D) all of them When a mass of 2 Kg is hanging to it, a spring stretches by 5 cm. If the hanging mass is tripled to be 6 Kg, the spring will stretch by ___ (A) 3 cm (B) 5 cm (C) 15 cm (D) 10 cm A ball is pushed and is placed at the end of a compressed spring. When the trigger is pulled and the ball moves, what happens to the spring PE and the ball's KE? (A) PE increases and KE increases (B) PE increases and KE decreases (C) PE decreases and KE increases (D) PE decreases and KE decreases

Explanation / Answer

8) torque= force * distance

torque =80 Nm

distance =0.8 m

force = torque /distance =80/0.8=100 N

so the answer is (D) 100N

9)The first ball is thrown horizontally ,so its vertical intial velocity is 0 .The second ball is a freely falling body (intial velocity 0).so both the balls are eqvivalent to freely falling bodies in the vertical direction . So both bodies reach the ground at same time .

But first ball has a horizontal velocity at the time of projection . so the net speed in the resultant direction is greater than the net speed of freely falling body .

so the answer is (C) ball A has greater speed when it reaches the ground .

10) when ever a rigid body is pivoted and force is applied at a distance from pivot on the body torque comes into play . so we apply torque in all the cases .

so the answer is (D) all of them

11) pascals principle is based on law of conservation of energy .

12) when a mass is loaded to spring . the spring force equals the weight of the body

mg = kx

m is mass , g is accerlation due to gravity , k is spring constant , x is the displacement of spring from its equilibrium position .

here m and g are constant .so mass is derectly proportional to x .

displacement = 5 *(6/2) =15 cm

so the answer is (C) 15 cm

13) As the trigger is pulled the spring tries to come back to the equilibrium position .so when it does that it loses its potential energy . where as the ball attached to it gains velocity as the spring pushes the ball. So the ball gains kinetic energy

so the answer is (B) PE decreases and KE increases

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