Pseudo Force - NEET Physics Questions

Question 1:

A block of mass m is in contact with the cart. The coefficient of static friction between the block and the cart is ü. The acceleration a of the cart that prevent the block from falling will be

neet pseudo force questions

1. a> (mg/ü)

2. a> (g/ü.m)

3. a ≥ (g/ü)

4. a ≤ (g/ü)

View Answer

The condition to prevent the block from falling is that the friction force must be at least equal to the weight of the block:

$f_s \geq mg$

Since static friction is given by $f_s = \mu N$ and the normal force is due to pseudo force $N = ma$ , we get:

$\mu ma \geq mg$

Dividing both sides by $\mu m$ :

$a \geq \frac{g}{\mu}$

Thus, the required acceleration of the cart is $a \geq \frac{g}{\mu}$ .

Question 2:

A truck is stationary and has a bob suspended by a light string, in a frame attached to the truck. The truck suddenly moves to the right with an acceleration of a. The pendulum will tilt

1. To the left and angle of inclination of the pendulum with the vertical is tan-¹(g/a)

2. To the left and angle of inclination of the pendulum with the vertical is sin-¹(g/a)

3. To the left and angle of inclination of the pendulum with the vertical is tan-¹(a/g)

4. To the left and angle of inclination of the pendulum with the vertical is sin-¹(a/g)

View Answer

When the truck accelerates to the right with $a$ , a pseudo force $ma$ acts to the left on the bob in the truck's frame. The bob reaches equilibrium where the tension components balance forces:

$\tan \theta = \frac{\text{Pseudo force}}{\text{Weight}} = \frac{ma}{mg} = \frac{a}{g}$ $\theta = \tan^{-1} \left(\frac{a}{g} \right)$

Thus, the pendulum tilts to the left at an angle $\theta = \tan^{-1}(a/g)$ with the vertical.