a body will speed up if -a) velocity and accelaration are in same direction.b)velocity and accelaration are in opposite directionsc)velocity and accelaration are perpendicular to each otherd)velocity and accelaration are acting at acute angles with each other.HINT - answer is option a and d. can anyone help me out please.

Correct options are (a),(c),(d)

Simply a body will speed up when there is a component of acceleration in the direction of the velocity.In both (a) and (d) cases, a component of acceleration is in direction of the veolcity which leads to the speed up of the body. In option (c), it will develop a velocity component perpendicular to the direction of existing velocity.(Vertical Componet increse and so does the overall velocity as wel as speed)

In situation (b) the body will deaccelerate and speed will receed

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THE CORRECT ANSWER IS A C D BECAUSE THE BODY WILL MOVE ONLY IN THE DIRECTION OF ACCELERATION

Hi Goutham,

Please note only (A) and (D) are right options.

These kinds of questions as generally asked in IIT-JEE where students generally tend to miss out some cases/concepts.

Please note that (C) cannot be the right option in all cases.

Consider a body uniformly moving in a circle. The acceleration is perpendicular to the velocity at all instants of time, but still the speed of the body is a constant. So (C) is not a right option.

Only (A) and (D) are right options.

Regards,

Ashwin (IIT Madras).

Approved